I had a small team that needed to share documents related to a consulting project. Everybody needed to use MS products, access it from the web, be able to check-in/check-out files, have a common calendar, a team blog, and a quick wiki for client-related information.
Sharepoint did all of that, in an integrated fashion, right out of the box. We got it hosted for about 30 bucks a month.
In addition, everything is an RSS feed. So as people change things on a thread you're watching, you can catch it right in your RSS reader.
If you have a few offices or remote users it is really useful. Probably not even worth considering for less than 15 people and only if you have some existing infrastructure. For smaller teams a hosted solution or some of the other products mentioned might be a better fit. (123together.com and intermedia both are OK for hosted SharePoint/exchange etc) Also, the blog and wiki stuff is still sub-par but the check-in check out stuff for documents does work pretty well.
I hate to come off like a fanboy, but I understand what Microsoft is trying to do with SharePoint and it makes sense to me.
I had another team that was just 2 or 3 guys working on a startup. We used basecamp and were very happy with it.
It depends on what you want and what your skill level is. If you're highly distributed and do a lot with Microsoft documents, then MOSS is a logical choice (and not extremely expensive). If you're just a couple of guys kicking around some code? Hack something together or use one of the simpler tools available on the web.
I'd draw the line somewhere around 4 or 5 guys, not 15 -- if you're doing something that's document-heavy. If it's just programming? I wouldn't consider it until I reached the 8-10 person team size, at least.
What part of that do people not understand?
Seems like you already have some sort of point or answer you're trying to get to. Perhaps it is "Microsoft sux and hackers can replace SharePoint!"
If so, then get to it. That Billion-dollar market awaits you.