There's quite a lot of really good suggestions on there though I didn't look at all of them (there's over 4000 according to site manager). But I did run through the first few pages to get an idea of what people are suggesting.
Some of my favorites:
Cross Game Voice Chat
Software Emulation for PS2 games
Trophy, Presence, and Profile APIs
Trophies for PSP
DLC Trophy Sub Folders and Progress Bar
In addition to these there's several entries requesting trophy patches for various games (Heavenly Sword and MGS4, please) even though Sony has no direct control over the developers of some of the titles.
You can always share your own ideas by heading on over to the PlayStation.Blog Share site.