I know that since I have joined Web Applications and gained the respective rep points I have tried my best to regularly clear the review queue for First Posts and Late Posts. I try to flag these types of posts as spam when I encounter them.
I have noticed that when I check these users profile they usually have only been members for a few hours and they usually have more then one post that are almost identical to each other advertising their sites/products with no disclosure of affiliation or real reason for recommendation.
Almost all of these types of posts end up in the spam box for moderators or the edit queue (for me at least since I don't have instant edit abilities yet) since I have edit in a description of the product/service/site being advertised after a visit to their site.
As Alex noted in the comments section above, some of the spam flags are getting rejected. I do not think that any of us see it as intentional, but rather as more due to the mods having enough work load that they do not see the same reasons to the flag as those of us with few responsibilities. I do think it would be extremely useful to have a comment box to add a reason and note to the mods as to why we believe that it is spam. It may also be useful to have a see also box were we could add links to the user's other posts that repeat the spam. I really do feel that this would help to clarify and improve the spam reporting and removal.
I am not sure exactly what the best solution would be, but one other starting thought to help to try to curb this a bit, is that we could try to implement a no external links on a new users first two posts or before at least one upvote or during the first 24 hours. These are of course only starting thoughts and obviously would need more opinions and thoughts on them.