I do seem to find 2 types of users of GT5p on this forum:
1) The players, looking for new things, getting through levels, etc... => It seems they quit GT5p and moved on to other thrills.
2) The simulation drivers, looking for improvement of their driving, getting fun out of comparing to others, etc... => They seem to chose one simulation and stick to it (can be GT5p for some, Ferrrari (now Supercar) challenge, ....)
I believe I'm in the category 2. I also have "Grand Theft Auto IV" but just do not find the same motivation then to take a car and push it and me to the limit in GT5p.
Must be 4 months now that I did not move the CD out (did not rent any Blue Rays recently) and need to cut down at the time I spend on it.