I usually leave GPS on anyway, but since I don't use many apps that make use of it the GPS battery consumption should be negligible. I don't usually use wifi either, because there aren't many free wifi spots in Japan and I come and go all the time
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I do however listen to music a lot over my bluetooth headset and it can go for hours losing only 5-10% with full 3G data connectivity.
The screen is consistently by far the biggest drain on the battery, so from my testing so far, as long as your screen is off most of the time the battery life is decent provided your 3G connection isn't constantly active e.g. real time polling apps.
I'm still doing the test for wifi-only with a lot of chatting/emailing/syncing, but so far so good.