There hasn't been a set release date for GT5.
Kaz is a perfectionist, so he will want the game as perfect as possible before release.
Also, will people stop complaining about the time... Please.
GT3 EU release was July 2001
GT4 EU release was March 2005
GT5 EU release is likely to be March-July 2010
Since GT3 we have had an average of ~4.5 Year's release times for each GT game to have a full release. Considering that PD have also been working on Tourist Trophy, GT HD, GT5: Prologue, GT PSP and GT5... I'd say the time taken, along with the content (1000 cars, WRC, Nascar, damage, tracks, PS Eye stuff... etc.) is just about right.