Apps and settings are probably the main things that cause the system to go laggy and inefficient. Other than that, reset also cleans up stock app caches, making them more efficient as well. Just like when you first got your phone with zero apps and data on it.
cheers for the reply. So i've done the reset (via the 3 button combo) and no luck, battery is still dying very quickly. i installed android assistant (for its app power consumption monitor) and it looks like the stock email app is using the most power at 6% (of the power consumption of all apps).
I just killed this and am about to kill app by app to find the offender.
on the plus side the lag seems to be gone!! looking forward to gingerbreads release though.