Just as a tangential point here, if you're coming from an E90 you WILL get pissed off at the N900's keyboard, as it's shockingly small, cramped, and bad compared to the E90's. It'll take a lot of getting used to.
Also, depending on your usage and amount of research you've done, be aware that Maemo has some significant functionality impairments compared to your E90. Most significant of these is probably email functionality, the N900's Modest install isnt a patch on even S60's default mail client, let alone ProfiMail.