It depends if you are just using it as a drive that stores your Operating System and Programs, or a drive that you will actually be working from and accessing frequently (aka moving photos on and off the drive). If you are just using it as a boot drive/program storage...the non-pro will be just fine. However, if you will be working directly from the drive...if you can spare the extra money for the Pro it certainly wouldn't hurt since we Write speed is much faster. The 840 Pro is a very highly regarded SSD, and the non-Pro is still unproven as such.
With that said, most people will agree that if it is your first SSD ever, and you stick with the non-Pro, you will still think it's amazingly fast and not even consider upgrading the Pro version.
Like zohar0 above, I too purchased the 256GB Pro version last week from Newegg at $199.99 with Free Shipping (and no tax).