Although 3G is more power hungry than 2G, all 3G Nokias I've used have a "use packet data = when needed / when available" option.

If you set it to "use packet data = when needed", the battery seems to last quite a bit longer, even though it's still a 3G connection.

I've noticed handsets supplied from 3 (the operator) have that set to "= when available", so the first thing I've done with several handsets for different people is change that setting.