Is there any way I can take a YouTube video and remix it, e.g. take a bit from minute 1 and a bit from minute 3 and put them next to each other to create a new video "collage"?

don't think do but that'd be really cool. or even use segments from different videos! it's a great idea-- somebody call google! :P

PS: And I don't mean this thing http://www.youtube.com/ytremixer because it's so slow it never loads for me...

The only way I know is by downloading it and editing. Gruelling and boring, I know. Maybe this could be your next project Philipp!

I can download at e.g. http://keepvid.com so ... hmmm, you make me realize what I'm really looking for is an FLV editor then.

Does anyone know a good FLV editor? (It's always risky to just download whatever EXE you find through Google...)

Well, maybe you could get SUPER http://www.erightsoft.com/SUPER.html

Downloadable here [this link will initiate the download process] http://www.erightsoft.info/GetFile.php?SUPERsetup.exe

and transcode them to another format. SUPER works easily. Then edit the video's and upload again.

(The super website sucks and It's hard to find the download so I posted it here for you)