In the VSE you can make proxies of:
AVI movies
Quicktime movies
But
Add an effect to media, make a meta strip and generate a proxy.
Meta strips with AVI contents work (sometimes)
Meta strips with QT content don't work
In this youtube clip I demonstrate that proxy function works until I make a meta strip.
http://www.youtube.com/watch?v=jvi-Rjm0SNI
Windows XP pro
2.61 r 44020
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Not sure i understand issue from your video correct, but issues with metastrips were just solved in rev44177.
Please check if your issues are indeed resolved in this revision and if issue will happen again, i'll need more exact steps of reproducing this issue with sample .blend file because failure might depend on specific setup of custom dirs, proxies used for preview and so.