I've been using a 500GB 840 Series SSD in my MacBook Pro for a little over a month now. Previously, I had an OWC Mercury Extreme Pro 128GB SSD in this machine and I don't see any difference in speed. I was expecting a slight decrease in speed with the Samsung, but SSDs are so damn fast that I can't tell a difference.

The long-term life of the 840 non-Pros are in question due to the memory chips used. The last review I read said it would take the average user 20 years to put enough data through it to wear it out. I don't expect this drive to be in active use after even 5 years, so I feel safe.

The 840 certainly has a big price advantage, and it's from a well-know brand of SSD manufacturers. I say go for it.