I tinkered with it a bit and I managed to make it work:
-for wishlist: ctrl+a, then ctr+c, then ctrl+v in "get from gog" maGOG button
-for library (owned items) it's a little bit trickier: in firefox, hit the Alt key, select File, click Save page as... select save as type: txt, text, hit Save. Then rinse and repeat for the second page of your collection, the third page, the n-th page of your collection.
After this copy-paste all the contents in those text files, one after another, in the "get from gog" maGOG button.

It worked perfectly for me and the databases correspond one with the other (gogs with maGOGs).

A somehow "fix"until mrkgnao manages to make it more elegant ;)

Great work, mobutu! Thank you.

Hopefully, by the time I get to this, GOG would have implemented support for variable number of entries per page.

UPDATE

I have re-enabled the scanning for downloadable file changes, now supporting the new account system. Reports as usual in the "what did just update?" thread.
I still have work to do (first and foremost the "Get From GOG" feature).
I hope to be done by next weekend, at the latest.

One simple way of copying a user's list of owned games: /user/data/games
(add after the domain name. Apparently I don't have enough rep to post actual links.)

Well, "simple", as it only has the games' ID numbers - and at least mine shows some that I'm not sure even exist... The lowest ID I've identified is 4 for "Descent: Freespace Battle Pack", yet I also seem to have 1, 2 and 3?

Nice!
How did you find out this url?

P.S. 1,2,3 are the three Fallout games.

I think I noticed it in a Javascript file while messing around with Firebug. :-P

P.S. Thanks! I've been looking up the IDs with a script that's part of the GOGmix editing page, and therefore doesn't include removed (or unbundled) titles... Is there a comprehensive list of them somewhere?

Cool finding!
Will this help simplify\improve some Magog script?

P.S: Magog knows the entire list ; )

Ah! I now see there's a convenient downloadable database too.
I must've been too overwhelmed by MaGog's interface to notice it at first.

I see you have found MaGog's exported database in text format. Good.

Note that it does not include the IDs of subgames within a bundle, nor the IDs of a dozen or so old removed games (which carry a negative ID instead).

P.S. If you happen to find that Javascript file again, do let me know its name and location. Thanks.

https://www4-static3.gog.com/js/54aa2e4-8e21abb.js

Thank you!
A veritable mine of useful links!
+4.

ANNOUNCEMENT:
Version 5.0.0 has been released with the following features:

* Rewrote large portions of the code that harvests downloadable file data from GOG to have it handle the new GOG account system
* Redesigned the "Get From GOG" feature to have it handle the new GOG account system [many thanks to plagren and mobutu for their help]
*** Note: Initially, expect a fair amount of unidentified games, especially new unbundled games, kickstarter codes, etc. (but these should be solved by you reporting them to me).
*** Note: Later on, as games are released on GOG, there will be a trickle of a few unidentified games here and there, for MaGog no longer has the wiki to learn from (but ditto).
*** Note: One advantage of the change is that now MaGog is able to identify owned premium editions and DLCs.
* Added language display for tarball archives and language packs

well that was buggy. when i clicked on the forum button, it opened up like 6 forum tabs and i can't close most of them. weird ass bug.

I'm sorry to hear that. Can you elaborate a bit. What exactly did you do and what were the symptoms? Which browser did you use?