how many cores?

i5 CPU got 2 cores, click on Apple logo, About This Mac, more info. There you will be able to see the number of cores as well. i5 and i7 CPU' support Hyper-Threading which means you got 2 physical cores and 4 virtual cores.

and just for the record.... an apple genius told me that i can replace my RAM without voiding the computer's warranty.. only the RAM won't be covered anymore... is that true to anyones knowledge?

Yes, that's all true. Of course even though your RAM won't be covered by Apple's warranty, it will be covered by its own manufacturer's or vendor's warranty, which is typically a lifetime warranty on RAM (as opposed to Apple's one-year warranty).

If you damage anything in your MBP while installing RAM, the damage you cause will not be covered by your Apple warranty. But replacing RAM is very easy, and that's why Apple prints instructions for doing so in the owner's guide that came with your MBP.

No, it isn't "bad." It's what it is. It's fewer cores than 4 or 8, and if you could get 4 or 8 cores in a MBP, it would be faster than what you have. But you can't, and the likelihood that more cores would actually benefit you in any of the work you do on your computer is very close to zero. Don't worry about this.

and what if I am running my mac with 2 or possible 3 virtual machines (my norm is 2, mac, XP and Ubuntu (the third I bring up occasionally is Windows 7)) at the same time? you're telling me 4 cores won't help?

Yes, with all that resource-hogging overhead, you could probably benefit from 4 or more processor cores, just as 0.00001% of the populace could benefit from a 700-HP, 220-MPH Ferrari. Most folks, probably including becks87 who raised the question, never come close to taxing their dual-core processors or their Toyota Camrys.

There would be no way to adequately manage the thermal tolerances of Intel's previous quad core mobile i7 processors in a package like the current MacBooks. Every machine with a quad core i7 is much bulkier. I'm not fully up to speed on Intel's new Sandy Bridge architecture... so I'm not sure if they're less "space heater" like.