I have the S Center and like it rather well. It has a nice sound and seems to do a fine job of handling dialogue, etc. Audiophiles will surely jeer, but it does the job just fine for me.
I had the S26 and I think they are great bookshelf speakers. Absolutely one of the best speaker value out there. I never really tested their limits given my listening room is a small den (I was using them as L/R speakers). I don't think people give JBL its dues for designing an inexpensive, yet high quality, series of speakers that are great for both music and HT. Some of these people have their small minds made up before even listened to the JBL's.
I have the S center, S310's, and S38's, very nice "rock" speakers for lack of a better term. The s38's are almost overkill for the rear, you could go with 36's or even 26's for rear.
There was a write up in one of the audio mags on the 38's and they raved about them, very accurate, and play very loud. You could use S38's fronts, S26's rears, wait for the center till you have more $$ and get a SVS 25-31 sub for a killer (about) $1100 speaker system. ( If you don't have a sub yet) I would buy what I have now over again, but if you have a tight budget, I/d do the above.