MacBook Pro text display problem

Hi there,
I had a MacBook Pro for 10 months now and it performs very well most of the time. However, my problem is that the text in the interface will occasionally become very weird. For example, Fi d r, where some of the letters are missing. Not only does the main interface have the problem, as well as my msn and all the applications. I wonder does anyone encounter the same issue and is there any way to resolve the problem?

Thanks
Lilly