I recently posted about some issues I've seen so far on a different thread, but realized it might be better posted here.
I have actually experienced some VERY bad lag, but I think this is due to my using LauncherPro. I'm coming from a Droid X that was rooted and it was having similar issues that I'm seeing on my GN, so I'm thinking it has to be an app that I have.
Currently, my GN is rooted and bootloader unlocked, but has no custom roms. The lag I'm seeing is when I'm opening up the app drawer, there is very noticeable stuttering, though scrolling is still smooth. Sometimes switching between home screens, there is considerable lag, as in you'll see the animation get 'stuck' for a second or two before completing. I wanted to make clear that the lag from the app drawing and changing home screens isn't constant; I'm not sure how to trigger it, but it has happened on numerous occasions.
Another recent issue was being unable to change the wallpaper; I could change between a few of the live ones, but changing between the normal ones sometimes does not work. For instance, my wallpaper will become entirely black OR I'll be stuck on the current one, which seems to me that it could be trying to change the wallpaper and simply failing which in turn could be affecting the performance.
I also use Beautiful Widgets and I have seen when suddenly, ALL the widgets on all home screens suddenly crash (it'll give me some error message like 'problem loading widget'), going into the app drawer and between home screens becomes excruciatingly slow, I can't even delete the widgets. I haven't been able to find a resolution for that aside from rebooting.