Darkspore is no longer being sold on Steam, reports GameTrailers based on a comment on NeoGAF, and sure enough, a Steam Search for the title comes up with listings for the demo and a trailer, but following either link just redirects to the Steam support page (thanks nin via Kotaku). They say since its launch, Maxis' sci-fi action/RPG has suffered intermittently from Error 73003 from being unable to connect to EA's servers, and more recently a new Error 3 popped up, preventing players from saving changes to their characters. Darkspore is still being sold by EA's Origin, so the game may be temporarily off Steam to work this out, as pulling the game after 26 months following the Error 73003 issues would be a strong indictment of the game's reviled always-on DRM scheme. And although EA may yet be addressing this, according to a statement on the Darkspore Forums, developer support for the game seems to be at an end, oddly, referring inquiries to EA Customer Support, even though it's an EA site:

Darkspore is no longer developed. It is for almost all intents & purposes an abandoned title. If you cannot play the game & have flicked through technical issues for any fixes, then contact EA Customer Support; especially if it regards CD-Keys or refunds.

Error 73003 has gone unfixed & remains an issue.

Error Code 3 has arisen for the majority/all & remains an issue.

I will however keep the forums here as clean & tidy as possible in my spare time. Why? Well why not. If it helps anyone with minor problems, or find their way somewhere, then that's great.

I wish you all luck, no matter what path you choose with Darkspore.