I just talked to the receiver last week.
The holdup on the second payment has been that Penson and another creditor were contesting the receiver's plans. The "good news" is that the receiver has settled with one, and is close to settlement with the other. The receiver said that they have sent the settlement papers to the latter, presumably based on at least a tentative agreement. When this is completed they will make the second and final payment to the traders.
The person I spoke to said the second payment will probably be in August, and be in the 20-35% range - which is what somebody else on this thread heard. So we're looking at 60-75%, if all this is to be believed.
Hope this helps!