Stayed at Guner's place for 4 nights in August 2014.
First of all the communication with Guner was amazing. Even though i live in Australia and the time difference is 7 hrs he was responding within a very acceptable time frame. Loved the fact that it's a clean self contained apartment with all the appliances (kitchen stuff, hair dryer etc.) Aircon was the saviour!
Location is good. Though if you are a female travelling on your own and planning late walks back home (after 11pm) I'd be a bit concerned. But to be fair, you can always catch a cab as an alternative (max 10 tl from most of the places in Beyoglu).
Taxi to Havatas in Taksim (airport shuttle) was 6.5 tl for me as well.
There is e2 channel on tv if you need some entertainment in English.
Guven was very helpful with like... everything.
Happy birthday again buddy! ;)