now they have these different SMP clients... and I am like uhhh... which one do I use... I could search.. but that would not be as fun
besides, I have done my helping of people in the past...
Someone want to throw me a bit more detailed bone?
There are 4 different SMP clients available to download. The first two, Mac OSX and Linux, should be pretty self explanatory as to where they fit in the picture. The second two are Windows clients, one which uses MPICH and the other Denio. Those are just two different libraries (really, just 2 different implementations of the MPI standard) that accomplish the same goal, utilizing multiple CPU cores. Under the hood, they're actually more similar than they are different.
So what's the difference and why do we need both? The Denio base client is newer and addresses multiple issues with the older MPICH client. Its more stable and more likely to "just work." However, the Denio client cannot run on 64-bit editions of Windows, so they have to keep the MPICH based client around as well since it does. These clients are both beta, so they have a set date in which they expire built into the program. At the end of the page, you'll see two replacement executables (one mpich and one denio) which are replacements that you just drop into an existing installation with a later expiration date. But you'll still have to drop these in after a new install still IIRC.
The Linux and Mac clients (which are pretty much the same) absolutely kill the Windows clients (either one) as far as PPD is concerned. It's also considerably more stable and simple to set up. These two reasons are why many (myself included) prefer the extra trouble of setting up Linux in a Virtual Machine and running the Linux SMP client there. As I said earlier, it can be a 35-50% increase in PPD. And the latest VMWare now supports 4 CPU cores, so a single VM will do.
You'll also find the GPU client which runs on any Nvidia card supporting CUDA (8000 series and later) or ATI card supporting CAL (it says HD2xxx and higher, but the older cards just can't hack it any more). You can run a copy of the GPU client along side the SMP client and really maximize your performance. However, the more complex of a setup you choose, the more of a performance hit you'll notice on your computer. As long as you have the memory to support everything you're running, it won't be a huge loss in performance, but it can be noticeable.