Originally Posted by cschang
While I don't think having matched surrounds is essential, I do feel that once you do have match surrounds, you wouldn't want to have it any other way.
That's exactly how I feel about the matter. Having lived with both options, I'll confirm that the surrounds are indeed the least critical in terms of timbre-matching, both amongst one another and with the front speaker, and that you can have quite a satisfying experience with just about any decent surround speaker. That said, once I started using a fully timbre-matched system, it sure didn't take me long to appreciate how seamless the whole sound field became. I used to notice my surround speakers more, but now I just experience the effect transparently--like a well-integrated subwoofer (which took me nearly forever to achieve in my HT, with numerous failed attempts), you don't notice that the speaker or channels are working, you just hear what you're supposed to hear.
When you're caught up in a movie the effect is perhaps more subtle than I'm making it out to be, but for critical listening (especially with multichannel music and how certain movies utilize the surround channels) it is surprisingly noticeable, and as cschang said, I wouldn't want to have it any other way (if I could help it). This doesn't stop me from recommending non-timbre-matched surrounds in certain cases, especially for those who would otherwise have to skimp on the quality of their front speakers due to budget considerations, but in my opinion striving for a fully timber-matched system (or close enough, anyway) is a worthwhile consideration--not the be-all-end-all, or even necessary, but still a goal to be weighed against other trade-offs.