I don't know what exactly you mean by '"active-suspend" support', but the N900 is really quite frugal with power when idle, with no user intervention required -- as soon as the CPU runs out of stuff to run, it drops to the equivalent of a laptop's suspend-to-ram, so there's not much use for any sort of manual suspend.

The trouble users have with low battery life stems mostly from programs that are actually using the processor (which of course does use power) while the screen is off, typically fetching updates or such, and the only "cure" is to stop them from running, which is IMO highly undesirrable, as it creates a traffic jam on wakeup, as the RSS reader, IM client, app manager, etc. all wind up going online and updating at once, rendering the system somewhat unresponsive when the very reason you woke it up was probably to do something now.

The other place you can save power in a suspend-like mode is to take one or more radios offline, eliminating the WLAN, bluetooth, and/or cell radio power draw, and also (depending if you leave any network links active) stopping apps from trying to update. This has been available under-the-hood (some tweaking required to activate instead of screen-lock) in the N800 and N810, and may still be there for the n900, but I never liked it -- you wind up waiting for it to reconnect, and then the aforementioned traffic jam bogs the CPU down again, then you get to do whatever you unlocked the screen to do.

IMO it's better to simply not use apps that grind unnecessarily when you're not using them, and/or to have options in the app that legitimately need processing (e.g. mapping software) to curtail/reduce activities when the screen is off.

Oddly, the 770, N800, and N810 all had just such a button on the front face, to the left side of the display -- I guess someone decided that bit of functionality wasn't as important as shaving a couple millimeters off the overall size.