Eh, I had to make this exact decision not too long ago. Ended up with a Lenovo T400 and I have no regrets. I based my decision on two main reasons:
1.) It was cheaper. I could pocket the difference or spend it on some nice upgrades (probably could have bought an ipod outright with the savings and still have come out ahead!
).
2.) I had no reason to need a mac over a PC for work/school at the time; Windows/Linux suited my needs just fine.
I could have just as easily gone with the T500, but I felt that the extra portability offered by the T400 would be kind of nice. Also wasn't terribly attached to having a larger screen.
With regards to SSD, it entirely depends on whether or not you can afford it now. It is definitely a nice upgrade, but I just feel that the price point is on the high side right now. If you can wait, I expect that prices will come down should you want the upgrade later. Hard drive replacement on a Thinkpad is a fairly trivial process anyways.