Generally speaking, no.
If your not aiming at very high resolution gaming (above 1600x1200) it won't be worth it. The best single cards of today can handle most games up to 1600x1200. If higher then SLI/CF is to be considered.
Multi GPU configs using cheaper GPU's is always a bad idea as a single higher end card will almost always outperform and be the better deal. Multi configs using high end GPU's is nice and will take the performance crown no doubt, but if you on some kind of budget I would strongly advise against it.