There is a method that allows for recovery of a 'wiped' drive but it is very costly and only has about a 25% success rate. For the common examiner one pass is usually enough to make it impossible for us to get it.
I haven't researched it but have only heard what I learned in my training but this is what I was told. I guess if it were a matter of national security then it might be worth a try but anything less than that it's not worth it. I believe the DoD is the only one that has the ability to do this. The cost I heard was in the $50,000 range.
There are different theories out there though. I know Gutman says 3 passes, DoD says 7 passes, etc. (this might not be accurate but just to give an example).
I know in my experience with the tools available to me, if it's wiped once it's out of my reach. I use EnCase and FTK, the same tools that are used by the FBI, police agencies, etc., so I know they can't get to it using those either. My instructor was/is a Cpl. with the PA State Police and handles all computer crime investigations in this region for PSP. He said in his 11 years of doing this they have never went past this stage. If it was wiped then they dismiss it and look for other evidence somewhere else.