I can't improve on this:

http://everythingsysadmin.com/2011/06/avoid-using-the-term-c...

That's precisely how we look at it internally -- IaaS, PaaS, and SaaS. We speak in terms of "the cloud", as coarse and imprecise a term as it is, because that's what a lot of the people we're trying to reach are thinking in terms of and looking for. Plus, it just flows more smoothly than "IaaS/PaaS/SaaS" in a headline. :)

I like the terms *aaS, but I don't they don't exactly roll of the tongue (either four syllables or a too generic term that sounds silly and is easily confused with other things).