Hmm, I don't have a particular corner where I'm always strong versus my opponents, it varies from race to race where other people are weak or strong. It also depends on what car me and my opponenets are using. But generally I seem to get a jump on people on the exit of turn 2 and heading into the start of the Esses, which sets me up nicely to take and defend the position all the way to Degner.
The 2nd corner/exit of Spoon is a good place usually to catch people, but I'm no master at it, its more that other people are weak there.
A favourite corner for me to overtake though is slipstreaming through 130R and then jumping past under braking into Casio. Its always very satisfying to pull of moves around there, as its at such high speed.
Edit: Oh thats a good corner too, the bus stop at Daytona Road is definitely a good place to make up a dose of time.
If I was to talk about all tracks and not just GT5
ones though, I'd definitely say turn 1 at Mugello (Ferrari Challenge), the turn 11-12 combination at the Nurburgring (F1:CE) and Maggotts/Becketts combo at Silverstone (FC & F1:CE) are strong corners for me.