I have have sereral GFI's trip repeatedly. I have replace one and it seems to be OK but another one that I repalced last year keeps triping. I cannot find any problems in the house like moisture or leaks. Do GFIs have a significant failure rate or should I assume I have an underlying electrical problem?

If you have wires on the load side, that may be the cause. If it works fine with out the load wires, GFI is likely OK.