Am I doing something obviously wrong?
DiabloMiner-Windows.exe -u username -p password -o bitcoinpool.com -p 8334 -v 2 -w 128 -f 15 -g 60
[4/6/13 10:36:56 AM] Started
[4/6/13 10:36:56 AM] Connecting to: http://bitcoinpool.com:8332/
[4/6/13 10:36:56 AM] Using AMD Accelerated Parallel Processing OpenCL 1.2 AMD-APP (1084.4)
[4/6/13 10:36:58 AM] BFI_INT patching enabled, disabling hardware check errors
[4/6/13 10:36:58 AM] Added Juniper (#1) (10 CU, local work size of 128)
[4/6/13 10:36:58 AM] ERROR: Cannot connect to bitcoinpool.com: Bitcoin returned unparsable JSON
DM is very flexible with the jSON it accepts. I suspect bitcoinpool.com is sending invalid work. DM does not yet support work without the midstate yet (its on the todo list but I've been busy with other things lately) so that could be the issue.
Use a different pool in the meantime, such as p2pool.