Speaking from my experience with the n900, I'd say my battery life is excellent on standby. Here's how mine is currently

GPS is disabled in settings.
Wi-fi is disabled.
Bluetooth is disabled.
I do not have the switcher for 3G and 2G. I only use wifi when I go on the internet. Any other time I keep it on 2G.
I do make calls an d text.

I only have 3 desktops enabled.
I have any widgets, mainly desktop execution widgets and shortcuts.
The only widgets I have that constantly update it self is from desktop execution widget. I have the widget that shows battery percentage and battery mah, I also have calendar widget enabled, and mp3 widgets.

I do not have email widget enabled as I recently forgot my password accounts ;D.

My screen is set to 3 out of 5 brightness.
I am running the default theme.
I do not have a Micro SD card installed.

I usually charge it, urghhh, whenever I feel like...lol
I do maybe one or two hours or more of internet surfing a day.



Ok now to get down to how my battery performs.

I've never overclocked, hell the n900 performs uber fast on default kernel :/.

On standby my battery goes down exactly 5% every 9hrs, I know because I keep tabs on it.

Gaming, (I use pico drive mostly), It goes down 10% every 45 mins.

Listening mp3's, battery goes down 5% every 2hrs, although it is to note that my screen is locked using the side switch, and I use qwerty 12's "extended locker" to switch through mp3's. And I only use the default media player :/. Although I have media box installed.

Browsing the net, battery goes down 5-10% every 30 mins depending on how heavy the webs sites are. I use only the default web browser.

When calling, I'm not sure as I never speak long on the phone, hate having anything up against my ears >_>, but can't imagine the battery life being terrible there.

Things to note:
1) My cpu is about 4 - 10% on standby (mostly 4%).

2) Using the side switch to lock the phone seemingly saves more battery.

3) I have only one daemon installed (extended locker).

4) I keep one of my 3 desktops free of widgets, why? Because I noticed that widgets only refresh when you switch to their desktops, thus reducing cpu. So before I start any application, I switch to an empty desktop.

5) I took off my keypad lights to save battery, I switch it on during the evenings though.