Check out the news page -- it's updated both with a new press release (including a couple short quotes from Frank Black and Kim Deal) and most interestingly, this:
The Pixies have rehearsed and they will rehearse again in March in a secret location in Los Angeles.
Yes, they have decided which tunes they are doing. For the most part, they'll be doing Pixies' tunes.
As for new songs, there's a Latvian lullaby, a Czech dirge and a Bulgarian ballad.
Bands play secret shows at small clubs under different names. My friends in bands tell me they do it in part sometimes to get around those contractual agreements. I wouldn't be surprised if the Pixies did that in LA. In fact, I'd expect it.