I never say, "I didn't really accomplish anything there." while interviewing. I usually just go with the work wasn't challenging and that it wasn't a good fit. Looking back, I wish I wouldn't have taken the position or I should have jumped ship sooner.
There are a few reasons for mulitple jobs in 5 years and I'm not going to get into them on here because I don't want to get into a flame war.
More than likely, I'll probably switch to contracting someday.