last time I had to call for reservations using a party of 3, every time it said nothing was available, the phone CM put in for a party of 4 & a reservation came up. She said it happened all the time, not an issue because party of 3 gets seated at a table for 4 anyway. Understand the online computer system glitches the same way - allows very few "party of 3" bookings even though there's plenty of 4-top tables available...it did for our recent trip (May 2010) when I was trying for parties of 3. Had to book a couple as party of 4, and no problem when we showed up with just 3 people.
Now I did just book a bunch of reservations (8 restaurants) in Jan 2011 for a party of 3 and it took all those with no problems. Course, that's still nearly 6 months out so guess the system still has availability for party of 3.