I've read 11 so far, which are the three books in THE FOUNDING omnibus, the four in THE SAINT and another four in THE LOST.

Book 12, BLOOD PACT, was released last year and Book 13, SALVATION REACH, is due in mid-2011. They are the first two books in THE VICTORY story arc. Based on the previous format, there'll be two more novels (taking the whole series up to 15 books) which will then be collected in another omnibus a few years down the line.

I'll probably stop at 11 and wait until either 13 is out and read the next two straight through, or possibly wait until the entire next arc is finished. Since the next four-book arc is called 'The Victory' I'm guessing this is where the Sabbat Worlds Crusade finally wins, although no doubt at great cost and only through great heroism etc

There'll be some kind of overview post about the entire series in the near future as well.

Abnett has written a number of other books in the WH40K universe but not involving the Ghosts, which I hope to get to in time. His EISENHORN and RAVENOR trilogies are highly recommended, so I daresay I'll try those at some point.