There is a lot of really good information at the link posted at the top of this thread.

I just finished about a week of riding around the Eastern (European) end of Turkey, including Istanbul, and I enjoyed my time there immensely. I posted some comments about my experience in this thread: Notes from a September 2011 ride through Romania, Bulgaria, Turkey, and Greece.

I was unaware of the different speed limits for motorcycles (lower than the posted speed limit), and I rode at the posted speed limit everywhere. Although I saw police by the side of the road from time to time, no-one ever stopped me.

Be aware that the toll motorway system requires that you buy a 'toll pass' (an electronic thing) BEFORE attempting to enter the toll road system. It is not always possible to buy this pass at the entrance to the toll roads.

I also found that the other drivers in Turkey were very aggressive, very selfish, and, to be honest, downright dangerous. You have to be fully alert at all times, expect the unexpected (translation = expect to be killed) from other motorists, and not assume that pedestrians will wait until you pass before walking out in front of you to cross the road.

Although the country is great - certainly one of the nicest countries I have ever visited - I think I can safely say is is easily the most dangerous country to ride a motorcycle in that I have ever visited. Turkish drivers make the Italians look like Germans by comparison.

Michael