I seriously hesitate to bother saying anything on this subject, because the other 3-4 times I have it's proven to be a complete waste of time. A lot of people on this board seem to have an addiction to misinformation.

Copy/pasted from a recent post I wrote that is highly relevant to you, since you're running the 15-inch unibody:

1) Some of the recent MacBook Pro models (I know about the 15-inch for sure, since I personally dealt with it) will have problems with replacement SATA-2 drives because of an odd problem with the onboard SATA controller. If you're seeing frequent beachballs and terrible performance in SSL ("running out of waveforms") after changing out the internal hard drive, you are probably seeing this issue. The fix, for now, is to downgrade the firmware...something that can either be done at the Apple Store or by finding an unsupported "downgrade" tool online.

2) Some newer hard drives incorporate "Advanced Power Management", which will cause them to constantly park/unpark the heads when installed in a Mac. The solution for that is kind of a hack:

mymacfixes.blogspot.com

This also fixed problems I was having with a new 2TB drive in my (desktop) Mac Pro.

3) The 12.5mm 750gig/1TB Western Digital drives WILL PHYSICALLY FIT into any current MacBook Pro. If you're seeing some kind of extreme performance issues after installing, refer back to 1 & 2 above. However, I still have reservations (as I've mentioned before in some detail) about whether it's a good idea to use these drives or not.

Sorry, the link got screwed up in my copy/paste:

mymacfixes.blogspot.com

The other problem is a real bummer, and is far more likely to cause serious performance problems (as in, audio and video both stopping as SSL "runs out of waveform". I'm not going to link to the unsupported "firmware-regression" tool here, as there is a very real possibility of "bricking" the computer if it's done wrong. The "safe" solution is to take the computer to an Apple Store Genius Bar (I know, ugh), where they are supposedly clued-in to the problem with SATA-2 drives.

All of that aside, I've been running the WD 640gb drives in my primary and backup laptops for a few months now, and have had no issues. I do have the aforementioned hdapm fix installed on both machines.

i have 2 640gb 5200 internals in my 17inch mbp. zero issues besides i dont have a cd/dvd rom drive now :)

I have installed Seagate Freeagent Go 2.5" 1TB drive www.bhphotovideo.com into my 15" unibody MBP and it was lagging. It took a very long time for any task to do. Even just to open finder it took like a half a minute or so. So I put back my original 320GB drive back.

^^ did you try out those fixes posted?

I have been experiencing the beach ball when watching some vids in quicktime occasionally. Is this because of the issue you mentioned DJ mark? Or is this normal when you only have about 90GB left on the hd?

I guess the real question, is eveyrone with the 15" affected with these problems or just its random?

Edit just read the link, so now i just have to check and see if im affected :). Thanks