BMW turbo charged engines are as reliable as any other manufacturer's turbo charged engines. I've had a 2008 535i and a 2005 PT Cruiser GT for three years and six years, respectfully--no issues with either. My 2011 X5 35i is one year old and it works great.
Most drivers/owners will never know whether they have a turbo charged engine or not, regardless of what brand they drive.
