Sample book covers: what do you think?

I'd go with the first. The title itself evokes a tag cloud. People who know a bit about tagging will catch that, and those who don't will already have a visual just looking at the cover of a taste of what tagging is about. The title is still very readable broken up that way. Congrats on the book!

Bobby

I'd also go for the middle one.
Although I don't like the bubbles and circles that much. It makes the book looking like one of those chemic books I was forced to read :-)

I vote for the middle one, too.

The first and the last are more typographically trendy. (Even though the Helvetica is classic, its de rigeur right now and won't be for much longer.) The middle one will look newer longer.

The tagline on the first is easy to read but hard to grok.

On all three I think the contrast is a little too subtle. Doesn't really "pop". The bookshelves are busy, so that's important.

No clear suggestion on how to remedy that. The yellow they're using is a nice strong yellow (plus this is on a screen and not in print, so there's a color shift).