I just got a Digilent Spartan3E board & tried to load a bit file using webpack 9.2 IMPACT says no USB cable found. Then I tried one of the JTAG3 cables from Digilent. IMPACT can see the cable but detects too many unknown devices. I'm guessing the board is just bad from Digilent. Now I go back & recompile everything for my Avnet Virtex 4 board. Using ISE 7.2 I get the same IMPACT error. Too many unknown devices. This Avnet board was working & I have used it a few dozen times but it seems to be getting flakier and getting harder to program.
So my experience is these xilinx fpga boards are not very durable or even working when received. ( Although I am impressed with how fast they are when they do work )
My question is How long does your fpga boards last when subject to repeated configuration attempts ? How long have you used a board before you have to replace it ?