Updated Libc.
Actually, it was interesting. I first put all the feeds, including 3.5.1 and after first updating ipkg to its binary form, performed an ipkg upgrade. It actually did a pretty good job apart from matchbox suddenly stopping working because of no fonts, something I'm sure is fixable (But I have no time at the moment).
However, just by being careful in the command line and update a few things, including libc, doesn't seem to break anything I use.
This is all with RC4. No idea about RC5 yet. (Just installed it).