Memory Cards.... Class 4 vs Class 10

All of my memory cards have been Class 4. I recently bought a 32GB card that is a Class 10. Class 10 is supposed to be faster and recommended for RAW shooting. Has anyone noticed a difference in the classes?

Only thing I've actually noticed was the record capability with a gopro cam. Using a class memory card that was not rated for the burst rate would tend to lock the device up.

I used to think the Class ## refered to the MB/sec write capability. So a Class 10 would have been 10mb/sec.
But the 2 32gb class 10s I just bought state they are up to 45mb/sec. (SanDisk Extremes).

However for my previous cameras (PS) I've never noticed. Havent tried out my nikon yet. Hopefully someone else will be able to add

Nikon recommends class 6 and up for video, class 4 with existing buffer technology should be fine for pictures.

My class 10 (PNY Pro) says it writes 20mb/s, my class 6 (sandisk Ultra ) says 30 mb/s ???

The class of the card, i.e class 10 refers to the minimum right speed of the card, so a class 10 card has a minimum right speed of 10mb per second,

Here's the recommended use of class 2 - 10 SD cards.

Class 2 for SD video recording
Class 4 and 6 for HD ~ Full HD video recording,
Class 10 for Full HD video recording and HD still consecutive recording

Thanks!
I was pretty sure it had something to do with the speed of writing.