Hmm. I changed jobs 6 times (5 companies) in 3 1/2 years, which averages to a job change every 6 months. Longest stint I had was about a year. As far as I can tell, I have not been noticeably penalised for it in my professional life.
It's definitely the fastest way to increase one's income, and you can't blame people for doing that. My first job was doing technical support (first full, then part-time) at $8.50/hr, and the subsequent 5 job changes were simply progressions to a very modest mid-level IT salary in the $50-$70k range. I don't think that's ridiculous.
Fair enough, but, it seems to me that it is rarely the case that two positions at two different companies in our field are truly the same, even if the title is the same and/or they draw on similar skill sets.
My jobs were all in different subspecialisations of technology, but there is a certain identifiable sameness that unites all of them, and especially unites the first three (ISP and SMB-oriented IT consulting work) with the last three (VoIP & TDM telecommunications).