Jrt posted some notes about using the Bus Pirate with OpenOCD:
It does work – but it’s not slick or fast. If you want a cheap JTAG adapter for remote debugging or big flash writes, get an FTDI-2232 based one. But, it’ll be fine for fiddling with bootloaders or just interrogating hardware.
We agree that the Bus Pirate is good for JTAG and flash tinkering, but once you get a taste you’ll want something built specifically for bandwidth-intensive tasks. We’re working on our own FTDI-2232 JTAG programmer, the Bus Blaster. You can read more about it, and contribute to development, in the forum.
Bus Pirates are shipping now for $30, including worldwide shipping.