The Maemo 5 icons are clearly vector-based which is a Good Thing. Windows 3.1 didn't have that hehe. The icons remind me of KDE (I'm GNOME user)... which is OK btw.

I'd rather not see too many sharp edges in icons though, which isn't easy, but something the iPhone icons do very well. I don't call that childish, although 'round' equates to 'female' aspects whereas 'sharp' equates to 'male' aspects, so I can see where such is drawn from, and I can imagine a business user wouldn't like such. What they do very wrong, is that they have that red icon for pending stuff like e.g. 2 e-mails (which is then totally not synced with IMAP server) while for example the Weather icon just shows a sun with 23c and the calendar also shows a date. The home screen is supposed to be informative yet these icons aren't! Not good...

PS: I hope you notice some of the 'roundness' changes in various aspects of the Nokia N900 and Maemo 5, I surely did! For starts the slight curve on left and right side of the device.