I have identical towers for my front L/R and surround L/R, and the center is a match from the same family. I run a 7.2 system, so the surrounds are not really the "back" speakers... they are the surround L/R and are located at the sides of my listening area. I have a completely different pair for my surround "backs".
For movies/TV, it sounds great. However it seems like a very small percentage of sounds come from the surround L/R, (and even less from the backs). I'm not convinced a less expensive pair of bookshelf speakers for the surround L/R would give me a noticeable degradation in the sound of movies/TV.
Now, music may be a different story. Most of the time I listen to music in stereo using only the front L/R and subwoofers. Occasionally when people are over and moving around, I'll use Multi Channel Stereo and it really fills the room nicely. Have just ordered an Oppo bluray player and one SACD to experiment with surround music. I suspect it will sound great, but don't anticipate buying a lot of SACDs, and regular CDs artificially split into surround by the AVR are just not my preference.
All in all, here's my recommendation: If you have the money, go for it. If you have to compromise on the quality of your front 2 speakers in order to afford 4 of them, skip it. Get the best front two you can afford, and spend less on the surrounds. You may sometimes wonder if a couple hotrod speakers on the sides would sound better, but if you buy them you may not notice any/much difference. Just my 0.02.
