On 2.1 (unrooted), the phone was great at first. After having it about two months, it became very laggy at times. Once I upgraded to Froyo, the phone is fantastic. Although I have noticed times when the screen would time out and then hang for a few moments before it would respond.
I am going to pull the battery a few times and then see how it responds. Like on my BB Storm 1 when upgraded to hybrid software, it could take a while before the phone gets used to new software. Overall, 2.2 is a huge improvement.