I've been playing around with some Web 2.0 services (Widsets, Yahoo Go etc) on a Nokia E71, and one thing I've noticed is that they kill the battery, as they keep going online looking for new stuff to pull down. Given that the device has a huge 1500MAh battery, the fact it can be depleted in a day (and gets pretty warm to the touch too) indicates to me that we've got a problem here.
Anyone else experienced this? Obviously the simple answer is to turn off "push" and "background apps" but that sort of misses the point.
The other option is to have something clever in the network, like BlackBerry or the new notifications server bit in the Apple system, which wakes up the phone when necessary, without needing it to keep "polling" the network.
I've also heard stories that power issues can completely derail the "mobile presence" model - particularly if you have a "live" address book with hundreds of contacts.
I haven't had a chance to look in detail at yesterday's announcement by OMTP of their BONDI platform for Web 2.0 on phones (I have a meeting with them scheduled for next week), but hopefully there's something in there which could help solve the problem.