I’ve worked with party poker since 2002 and the only problems i’ve had have been small. Whenever there has been a stats problem, it’s usually been corrected in my favor. They always pay promptly and if they mess up a payment, they correct it, usually immediately.
This last summer, their statement was missing about $5k of casino for 2 different monthss commissions, yet the money was showing on the summary stats. It took them over 2 months to sort this out but the result was that they found they had messed up 5 months, and instead of the 2 months ($10k) i was owed, they owed me over $25k. Dishonest programs don’t find you extra money, from reporting errors.
I can say that it’s often frustrating getting an clear/quick answer or getting a more detailed report, but they’ve always been great to me, even when my new player signups were down from their once great heights.
I’ve also found them easier to convert than other poker rooms.