A coder by the name of Eskil, distraught by a response from Spotify's support team that the company isn't planning any development on the Maemo platform, has taken matters into his own hands and built a client of his own on the platform.
It's based on the Despotify libraries that aren't entirely endorsed by the company but haven't been shut down yet either. Like other mobile clients, you'll need a Premium subscription to use it, and you won't get quite the level of slick presentation as with the official apps. It also doesn't seem to do offline playback, but for those with a Maemo handset itching for some Spotify action on the go it seems like a promising solution.
Spotify has confirmed to Pocket-lint that it has "no current plans" for a Maemo client, so if you want to get the music streaming service on your N900, then you can find out how to do so on Eskil's website. Be warned - it requires you to compile your own code, so it's not for the faint-hearted.