Even with Launcher Pro, other parts of the OS can be laggy. (Though Launcher Pro is amazing.) But I thing the more accurate term would be choppy. You don't notice it that much until you use another platform for a small amount of time. Then going back it is very noticable.

Gingerbread fixes some of the "lag" issues with the partly GPU accelerated UI, mostly noticeable in the notifications pull-down menu.

Opera Mobile (GPU accelerated), with a decent launcher, memory optimizations (V6 Supercharger, or a good Autokiller config), and Android will perform just as good as any other mobile OS. Unfortunately to get great performance Android needs to be rooted.

That is it. I find my android phone animation perfectly acceptable until I tried an iPhone. Even a Windows Phone 7 feels better. I really hope android 4 address this problem.