I usually get 3 full days (72 hours) before I recharge (normally with 10-15% or so left), though I'm a "light" user (only GSM, EDGE connected about 10 hours a day, WLAN 2-3 hours, mostly e-mail, NewsFlow and a bit of xterm).
ProfilesX
I use erminig-ng to sync with google calendar. Two local calendars <-> two google calendars. Works perfectly, although I try to avoid all-day events (different phones, different servers, different protocols -- they all manage to f**k up such entries) as well as repeating events (hey, life is less boring that way . I still have not tried syncevolution for calendar sync'ing (but I do use it for sync'ing with google contacts - works well except for a few quirks).
If you have Windows you can use OVI Suite to load as many countries as you like. Works well, but no voice navigation (but see the thread about it). I also use Marble and highly recommend it.
I wouldn't try to push it. Too low voltages, smartreflex and all those crazy speed/battery patches are just time bombs. I use KP47, MIN 250 MAX 805, voltage as in "LV" profile. No VDD1/VDD2. Never had a spontaneous reboot (but once had to turn off the N900 when testing an alpha version of Firefox, probably should have waited a minute or so).
Good luck and enjoy the N900!