I'm in the same boat. Applied to six schools, but still waiting to hear back from all. I just talked to my adviser about it, and she said some encouraging things as possibilities:
1) As FailedScientist said, it's good news for us because it wasn't an automatic no--those are sent out first, as they simple toss them on the 'no' pile.
2) You've made the list high enough not to wait list you (yet), but not an instant acceptance.
3) They're waiting to see if they can fund you--some schools will only admit candidates with funding or full funding.
4) They want to secure all the funding or most of the funding for you ASAP to make the best possible offer because they have a feeling you're going to be accepted elsewhere with just as attractive an offer (if not more so), and they are possibly concerned that you will not accept the offer right away if it isn't good enough--this is, of course, the best possible explanation, but according to my adviser and several professors it is completely within the realm of possibility.
5) Your application has reached the faculty without being cut by admins--good sign--and a few (or one) is rooting for you while others are trepidatious or are interested in another candidate that the other(s) aren't sure about.
Ultimately, though, there are three good signs for us both: 1) We managed to stay out of the instant 'no' pile; 2) at this point, it's almost certain that our applications have made it to the faculty; and 3) no news is, indeed, good news--we're still in the running.