Both Ext3 and HFS+ support Extended file attributes, but the two aren't compatible and this could cause problems. You'd need some way of mounting those ext3 file systems (OSX fuse?). Using fuse rather than native kernel drivers will be likely to involve some loss in performance. Plus if you use an SSD, will those filesystems support TRIM when accessed from OS X?
Perhaps you could try it for your ~/Documents ~/Downloads and others, but I suspect it would cause a lot of problems for /Applications.
Alex, thanks. I have no idea what I am doing right now and why the hell on earth I came up with this idea , but believe it or not, I have put my Applications on NTFS and it's working. I'll keep it as it is for some weeks and if it's alright, I'll move /Users too.
Great that you got it going. Sometimes the best way to learn is to try these things. Perhaps it might be good to keep in mind that in some cases security and other properties might depend on the unix permissions and extended attributes, even if the application appears to work o.k. without them.