I am currently running mostly stock software on my Nokia N900.
The relavent non-stock packages I am running are:
2G/3G selector widget
BackupMenu/BootMenu
OpenSSH Server
rootsh
my MCE clone
my Cell Broadcast SMS operator name widget replacement

Are there any software enhancements that I can install that will improve battery life? Will installing CSSU improve my battery life? Will installing a new kernel or BME replacement improve my battery life?

I keep my phone in 2G mode most of the time (unless I am doing heavy data usage then I switch to 3G with the 2G-3G selector widget). Does doing that help the battery life? (or would I be better off keeping it in 3G?) What about if I am passing through areas of low signal strength? (the train I ride on often passes through areas where my 2G signal will drop out completly or get very weak, would keeping it in 3G in those cases be better?)

Anything else I can do to get more battery life out of this thing?