A source is simply the place you got your information from. While Wikipedia might not be the greatest source, it is indeed a source, as much as an Ancestry Family Tree, a FamilySearch profile, or rootsweb page. All may be in the category of less than helpful towards proving genealogical data, but they do prove where you got your information from.
As it relates to citations, I put them in the same category. If someone puts in the biography "he was born x date in x place, lived x places on x dates, married so-and-so, had x children, and died x date x place." and then in the sources does a bullet list of sources including Wikipedia, then it would be presumed that somewhere in that pile of sources should be found where that information came from. That's not bad (it's better than "Family Records"), but adding <ref> tags and showing which source produced which bits of data is better, even if some of it came from Wikipedia. Even better (if you're using Wikipedia) is to look where "THEIR" data came from in the sources at the bottom of their page, and cite the original information.
But I see so few who actually use citations as it's so much simpler to just drop a link and leave it at that. Again, I'd regard that as a premium profile if they actually incorporated a full citation including a link and made it very clear where all their information originated.