Xilinx is the undisputed leader in FPGAs, but I'm not entirely sure how a merger with AMD helps anybody.
FPGAs are probabaly used by AMD to prototype their CPU designs: but FPGAs don't seem to synergize with CPUs, GPUs in general purpose settings. There was a Bing accelerator on FPGAs (IIRC, using the Intel / Alteria Xeon FPGA chip), but such products are very rare.
Xilinx does make money though, and AMD is kind of inconsistent with that. AMD's stock price is way overvalued (AMD has a bright future, but its trading >100 PE), so an all-stock deal seems like a good idea.