While thread currently does not particularly apply to myself as I tend to pre-order most new games via Amazon now, but I remember my days as a poor student I would avoid paying full price for any game with very few exceptions. One such exception was FFXIII-2. I bought that game, and played it day 1.
Nowadays I tend to buy games day 1 to support developers. I bought "Etrian Oddesy: The Millennium Girl" day 1 purchase despite not actually having played any others in the series so that develops can see at least 1 extra sale from more "Niche" Titles. This may lead to more projects being localized in the west in the future. Saying this, I probably wont get round to playing it for a long time either, as i'll play the 4th instalment before this one (Whenever that will be).
What sort of games do you buy on day 1? What are your reasons for picking them up day 1?