I spent a very long time researching them for Christmas gifts a few months back, and I came to the conclusion that the technology is just entirely too expensive and unrefined to justify it. For $300, you get about a 7-8" diagonal screen, crappy software, limited organization capabilities, and resolution in the 600-700 pixel wide range, which IMHO doesn't cut it for that price. If it was $50, sure. Or, if it was $300 and you got something like 1024 pixels across.

That being said, Engadget mentioned a few Philips models a couple months ago that seemed to be a little bit better in terms of price:specs ratio. Not sure if those are out yet, but they seemed like the next step in bringing the prices down to reasonable levels.

There was a company a while back that was selling half-decent frames very cheaply, but they were tied to their online monthly service for storing the photos. I don't know if they're still around. You can also find some high end models that have a ton of features and big, high res screens, but the specific brands come and go every year or so, and the prices are out of my range, certainly.