As long as it isn't a Flash game, I have no trouble (Flash games devour CPU cycles, ugh).
Well I will follow Wave casually and see if it ever becomes a compelling product for users like me. At this point, it looks promising but not universally useful a la email and IM.

Can't hit back/forward in a Flash object, no default (as implemented by browser/OS) right click menu, strange scaling issues in certain situations, no searching in a flash object if metadata isn't properly done and other issues keep me away from flash as humanly possible.

I agree. I shudder to think how GMail would have performed if implemented using Flash...
Flash appears to be an extremely inefficient implementation, especially with regards to video playback. Silverlight at least seems to have decent video performance. Also, I hate Flash's tendency to "capture" all keystrokes, which prevents me from using keyboard shortcuts in the browser after I've clicked on a Flash object.
Oh, and most importantly the whole "open and fully documented web standards" vs "proprietary and closed vendor-specific technology" issue...

Some of these issues have been resolved or partially resolved. The back/forward thing is now supported, more functional right-click menus are available, and scaling has been improved.
I should add that these changes are not retroactive, so new features must be added and will not simply become available in existing Flash projects.

Not to deviate too far from the topic but there are still major issues with Flash (like support on other operating systems that aren't Windows, not to mention 64bit plugins) that keep me from liking it.
I don't hate it as others, I just try and keep away from it whenever possible. For most things that can be done in flash there is an AJAX implementation available.

Aye, although I find most in-browser experiences to be woefully inferior to true desktop applications. Sometimes, the tradeoff is acceptable (email), but often, it is not (word processing).
Back to Wave though, I wonder if we will see some sort of desktop implementation for those of us who prefer true apps.

The API is open and available and from what I know there are a couple of Adobe AIR based apps in development.

Neato.

There's also a Firefox notifier plugin for when an update is made to a wave you follow but haven't tested it yet.

Well, I just tried to use wave a bit as an alternative to IM, and I must say the entire thing is very interesting. I *do* actually think that Wave might be the next generation of email. Still, there is a lot of polishing to do. It's kinda slow, and it's sometimes unclear when and where and edit was made, especially as waves start getting big. And the playback function is to clunky and slow to really solve this. If it was integrated better in the entire experience, it might work.
Also, it would be great if I could also check my normal mail from inside google wave. But I believe all of these issues already are on google's radar, so I hold high hopes for the future of google wave.

Sent.

Thankey!

As others have said, Wave is a limited application at the moment, but it definitely has potential. It all comes down to how quickly good extensions are released, and whether or not they add features like the ability to export/download a Wave or the ability to lock certain entries to be edited by only selected users (maybe something similar to private replies that can be sent to select users).