87ninefiveone :
Why not? The price for the FX series chips is decent, the motherboards are less expensive, and while they may not benchmark as fast as the Intel stuff they're perfectly fine for today's games. If your on a budget the Bulldozer chips are fine pieces of hardware. Besides, when is the last time anyone had 100% CPU utilization with their 2500K or 2600K in a real life situation?
1) Because, like I said, they are pretty much terrible. They take LOADS of power when OCed and the performance per clock is bad. Worse than Phenom II, so actually a downgrade in my opinion as the FX-8150's performance is on par with the 1100T when being stressed to the maximum, meaning that 6 cores worth of PII at a lower clock is stronger than 8 cores of FX at a higher clock.
2) Motherboards being less expensive is a myth. You can find Intel boards for just same price if you actually want one worth having. I know I wouldn't spend just $100 on a board if I wanted SLI/CF and the ability to OC well. You need to spend more money to get that anyway whether an AMD or Intel system. If you buy a h61 board, that is a pretty inexpensive board.
3) Yes, they are GENERALLY fine for most things, but the bottleneck many modern multi-GPU set ups and are very restricting in games becasue most games can only use up to 4 cores anyway. The FX quad cores are not very strong especially in games such as SC2 and BF3. Basically any CPU intensive game. Why buy what can scrape you by when you can get a CPU that will last you years to come?
4) 2500ks and 2600ks can be used to the maximum when you are doing video editing, running a CPU intensive game and other programs and just multi-tasking like crazy. Especially during explosions in games when the CPU needs that extra boost of power to maintain high FPS.
Those are my reasons why I do not think FX is worth it. I am not an Intel fan-boy, I love AMD, but they just are not worth it right now. You gotta buy smart, not on brands.