Well IMO, the first things that come to mind regarding redesign problems are iPhone 4 with its antenna connectivity issues (big flaw there,) or the Snow Leopard release (I think it was SL) where many users upgraded and lost all of their data - forced to do a clean upgrade I believe.
Not the best examples off the top of my head, but perhaps they'll give you some insight. Honestly, I purchased the last version of the pre-unibody MBP (mid-07) right before the upgrade, and yea at first when they released the new design I was sad, (I'm a product designer - appearances matter!) but I look back now and appreciate my decision b/c I've had less computer problems than colleagues working on early '07s or the first gen unibodies...
What people say about the later versions are true - the flaws have been fixed, the kinks resolved. Also, today I too placed my order for a newly updated 15.4" 2.2GHz MBP. I contemplated all the issues that [I'm sure] you're considering, and factors like time, current computer condition, price, and of course impatience and envy all played into my decision. The refresh is a good one and I'd say go for it if you need it and if you can shrug off/handle the tiny regret you feel when you see Apple's pretty pictures next year!