Have stayed there a couple of months ago. The hotel is great, definitely a must recommend - they just completed refurbishing the whole hotel, so the rooms are modern and comfortable and high-tech, with free wi-fi internet access throughout the hotel. The location is also a plus in my view - a ten minute taxi drive from the city centre's attractions, but right in the heart of the business quarter. Also is a minute walk away from Taksim Square, with all the bars, restaurants and shops available. In all, I would definitely recommend the Hyatt in Istanbul (check their site at istanbul.regency.hyatt.com).