Lots of people like them now, which is a significant shift in audience attitude from a few years ago.
When 3.0 was out, people complained about 5 level PrCs, mostly because they felt they didn't feel "complete enough".
I think at this point, people have come around to the idea that a PrC doesn't necessarily equate to a shift in career. Rather, they see PrCs as something which can serve many functions, among them the honing of a specific ability or theme. That's what 5 level PrCs do best - they give a player or DM the ability to fine tune a character along a specific path, without forcing them into the long term commitment of a 10 level PrC.
For what it's worth, I love 5 level PrCs when they are written to serve the above purpose.
Patrick Y.