Are you comparing Series 2 to Series 0 or something else? A S2 vs S1 direct comparison (with GPS off) should show longer battery life in the S2 based on the dramatically larger battery.
Also, as noted above, some of the battery draining features on S2, like brighter screen and GPS usage, can be dialed down for those who prefer to prioritize battery life and always take their phone with them, even when running.
I think the battery life has improved for
most with OS 3.1. Although, the S2 processor definitely consumes the battery life under loads. Before 3.1, the reports from other forum members were horrid.