I've just installed DD, post-patch, never played it before.
I'm running it on a E6850 / ATI4770 / 4 GB Ram rig on W7 x64. There is some mouse lag to the game, not big, but quite noticeable nevertheless.
I'm curious whether this is normal, or just a rare issue, and in case the latter is true, if anyone knows of a way to reduce it.
I've tried compatibility modes, and I am running it with UAC off.

Yes, I'm starting to think the same thing. It could be that indeed the game plays like this, but maybe some people don't notice it or just never pay it any attention.
I, for one, after the rigorous mouse-training that years of UT threw upon me, need only the slightest hint of mouse lag to feel like I'm trudging through molasses.
Almost forgot. Disabling desktop compositing does nothing, and any opengl settings are pretty much useless, since the game runs d3d. I'm thinking of giving that older config utility that some people mentioned here a try, and try to switch to ddraw for a change.
Later edit: Ok. so I've managed to get my mits on the old configtool.exe and changed the rendering to directdraw. Zero mouse lag at this point, so it's a definite fix for the issue. A glide wrapper would be worth a shot though, too.
Even later edit: No success with any glide wrapper that I've managed to find. Engine crashes. DirectDraw should get the job done, even if I've noticed some strange shadow artefacts using it.
Well this is as much a fix for this issue as it'll get, obviously. Too bad I can't mark my own post as a solution so others can get to it, should they run into the same problem.

Glad you found some sort of solution! Me being kind of stupid and all though i am not sure how to change the rendering to directdraw. Mind helping me out here?
edit: bah, didn't see that link you posted at first. Anyway, i downloaded the Divine Divinity demo, copied the old configtool.exe and switched to directdraw, and it worked! Thanks for finding the solution.
It's a shame that the moust lag input is present in the newer version of the game. Hopefully it'll be fixed.

You're welcome. The downside to this fix is that there's some quality drop in the lighting, and as far as I have seen, ddraw doesn't animate some flickering lights.

Yeah, I noticed the drop in quality but it's still worth it. I'll take responsive controls over eye candy any day :P

I too am coming across this strange issue. When I started playing there was VERY noticeable mouse lag. Not to mention that when I moved the character she walked EXTREMELY slow, even when running.
I started thinking that it was indeed possible that this was just the way the game ran, Which wouldn't make sense, but after watching some Youtube videos of gameplay, I seen that the characters move MUCH MUCH faster than what I was experiencing, Plus no mouse lag!
So, my question is, After reading through this forum it seems necessary to download the demo so that I can get the configtool.exe, But I have no idea how to obtain the configtool.exe from the demo, and further how to change the rendering to directdraw...
I can sometimes be quite computer illiterate, so if you guys wouldn't mind breaking it down for me I would be eternally in you're debt!

Phoboss, Thank you for the link, I was able to download and apply the configtool and am pleased to say that the mouse lag is gone and the characters now move with utmost speed and urgency!
Once again, thank you guys for you're help! I am now going to begin this grand adventure!

You are very much welcome. Have responsive fun.

I forgot to ask. Can you tell me please what graphics hardware and driver version are you using?

Hey!
Sorry it's been so long and maybe you have figured it out by now but if not, i will try to help just in case.
So, after you download and install the demo you will want to go to your Divine Divinity demo folder which should be located by going to Start -> Local Disc (C:) - > Program Files - > Divine Divinity Demo. In the Divine Divinity Demo folder you will see the Config Tool. It's got a little icon with three squares on it. Right click the icon and choose "Copy".
Next thing you wanna do is get it in the actual Divine Divinity game folder you downloaded and installed from GOG.com. So open up that folder by going to Start -> Local Disc (C:) -> Program Files -> GOG.com -> Divine Divinity. Right click in an empty spot on the folder and paste the demo's configtool in there. Now since you already have the original configtool, it will probably ask you if you want to replace it, or add it and delete the old one, or add it and keep the original. You will want to add it and keep the original so you have both config tools.
Now, click on the configtool you just pasted in there. ( should be configtool (2) ). You will see a bunch of options. In the second line under New Rendering System, you will see an option to click DirectDraw. Click that, then click Test at the bottom and wait for the test to finish. After it is done, click apply and close and you're all done! You can still change the resolution using the other config tool as well.
Good Luck! If you have any more questions just ask :)
EDIT: Well, nevermind, i didn't realize there was a second page so i didn't see that you already fixed it! (I'm stupid) Well, i'll just leave this post just in case anyone else is confused :P

I have a Nvidia GTX 295 with the latest beta drivers.

This solved the problem for me, thanks! Shame it's not enough to switch the rendering engine and keep the res high, though. I have to switch the rendering engine and bring the res down to the middle setting.

Are you saying you can't get higher resolutions while using direct draw? I'm fairly certain i got that to work but i could be mistaken.

No, higher resolutions were an option, but the framerate went to hell. =P

Hey, all. Glad to see this thread; I'm using CrossOver Games 9 for OS X, trying to get Divine Divinity running on it so I don't have to use my PC (loath to use it; every time I start it up I have to go through 20 minutes of updates to AV, Windows, Firefox, etc.! I just want to play!).
I'm on a Verizon capped wireless data plan here, so downloading the full demo of DD is a problem for me. Any way I can talk one of you into re-upping the configtool.exe from the demo to RapidShare? The link above is to a deleted file...
TIA!

This is from another post I made about the tool . . . just so you know the whole story . . . =) . . . link should still be good.
"Some folks have solved the problem using the old DD configtool.exe to set rendering to DirectDraw instead of Direct3D See this thread. You will see an early post in that thread from DeathKnight (a DD developer / programmer) explaining why they removed the option and plainly stating that it is not supported any longer. It is something that you would try at your own risk. It would only affect DD.
This link used to be good for the old configtool.exe Like I said, use at your own risk and some have claimed it fixed their problem."
Edit: you can turn auto update off for almost all products . .