I've noticed this morning a spam campaign that consist in editing posts that mention mails systems, portals like drupal, fb or related subjects to inject links to freeanalytics dot komfo dot com.
The problem I see is not that some spam could have be sent here, as I suppose SO due to its success it is a permanent target for spam, but that the spam has successfuly passed the reviewing process.
Only one or two reviewers rejected the edits, while the other accepted, and I reverted the edits after in the history.
I have the feeling that SO attracts so much flow and that many people that gained the power user rights did not spent enought time on the review process and accept too quickly some wrong edits. I know that the suggested edits are the review that spent the less time in the voting flow and often when I am doing some review, the time I am checking the edit contents and the given links (if any), when I vote to reject I am told that the post is already accepted (and like for the given cases, wrongly).
I know that some "testing cases" are sometimes injected in the review flow to check that the reviewer is attentive, and maybe that the process could be augmented to check if the accepting is legit based on the time to perform the review? Also the check could be aimed to the "rookie reviewers", as I also noticed that the less level a reviewer has, the quickest he is to accept wrongly edits.
BTW, IIRC the edits were anonymously submitted, that could also be taken into account to flag spurious edits.
EDIT: I would just make clear that my intention is not to accuse anyone or to find who is guilty for spam acception, but just to improve the process for helping reviewers and show them clues saying "man, pay attention that edit smells crap".
As it emerges from the comments on the Tim Post answer, it could result on a feature request to make the raw url more evident when a spam link is displayed in rendered output instead of markdown, because it is easy to miss it.