I use BalticMiles MasterCard since December 2009. Works flawlessly, good customer support and I am generally happy. Main benefit is no extra charge for purchases abroad. Main disadvantage is the limit per transaction.
I also earn BalticMiles in Neste. Works pretty good, too.
What does bother me is that time by time BalticMiles earning just doesn't happen. Last 5 flights over last 2-3 weeks didn't post. I e-mail them and got standart response back about retro claims. Since then miles post well. Will have to retro claim flights again...