I read someplace (no idea of the validity) that with Samsung devices running TouchWiz that a lot of the freezing can be attributed to the way Samsung did the file system. It isn't standard and therefor can cause problems.
Now, phone freezing in general can be attributed to the cache in many cases. Clearing out the cache on your apps and with some phones the call log as well can speed things up a bit. Sounds contrary to what you would imagine, but it works on plenty of the older phones.
The Nexus should not have the file system that other Samsung devices have had. I think they even changed that for the SGS2 as well.
My Droid Charge is running a ROM (GummyCharged) with the ext4 fs, so I had hoped that the reboots would go away. No such luck. I have noticed that when I use my phone for games, most of the memory get used up and it is more prone to freezing. No games=less freezes.
I really hope since google is in charge of the software for this phone, I won't be nearly annoyed be the freezing. Anyone here had the Nexus one or S. I wonder how those phones did with freezing?