Depends, some people see it as a worthy improvement, others are just "meh."
I believe Montevina will be the newest generation of the Centrino line - codenamed Centrino 2. I believe the biggest things with Montevina is the support for DDR3 RAM, improved Wifi, and WiMax (which has lost some momentum). One of the bigger things for me though, is the increase in battery life due to more efficient power consumption. Probably won't be much (as in, extra hour of battery life), but whatever.
Unfortunately, Intel has delayed Montevina to early August I believe (Previous launch date was sometime in July). Although it was already doubtful that Apple will release any details as of yet, the iPhone is it's biggest priority and I believe I saw something about the Mac Pro also, the delay makes it even more unlikely that we will have any information on a MBP refresh anytime soon. Most likely though, Montevina will be out by the back-to-school season, although I don't know if it'll be widespread. I believe that there are also some rumours of a redesign of the MBP, it's been using the current design for quite some time apparently.
So basically just follow the best piece of advice when buying technology - wait as long as you can but buy when you need it. No point in waiting for the next best thing since something is always right around the corner, but you'll still want the latest technology that you can get. There is a chance that the MBP will be refreshed before 9/20, but don't bet your life on it. However, Apple is generally quick in embracing new technology in notebooks, especially for their "professional" line, so it's likely.
Regarding the Mac vs PC shitfest:
Don't disregard Dell, they've gotten a lot better. In fact, their XPS 1530 is actually a very nice notebook, comparable with the MBP.
However, at the same time, MBPs are one of the few items I do like from Apple. Very slim, fairly lightweight, excellent battery life (for a 15.4" notebook), appealing aesthetics, standard LED screen, backlit keyboard, and decent graphics card. OS X along with the new touchpad (where you can do gestures and stuff) are also pretty nice. Didn't expect to like OS X much after having Windows for so long, and it was really quite refreshing and interesting when I played around with it. Of course, you dont have a large library of games to choose from, but that's why there is Boot Camp. Still, reconsider all of your options, unless you're completely set on having a MBP. (Just hope you don't get a lemon )