On average the main hotels usually start selling out around late April to mid-May. Then about halfway through June a bunch of people cancel their reservations, so a few rooms open up. Everything is generally booked solid by July, however. Sometimes if you get really, really lucky, you can get a room a day or two before the convention starts, since there are people who cancel at the last minute. That's how we got a room in the Hyatt last year.
I generally prefer to make reservations in March, since there are normally plenty of rooms left. Last year I left reservations to the boyfriend, which is why we got a room at the last minute. I'm not going through the stress of that again and am going to book the room myself this year.
Costumes for 2007: Ran (Texhnolyze), She-Ra (She-Ra: Princess of Power), Marie's Black Masquerade Gown (Sofia Coppola's Marie Antionette), EGA Plum Walking Suit (Original Design)
Cons for 2007: Katsucon (tentative), Animazement (tentative), MomoCon, Dragon*Con, Anime Weekend Atlanta