Bookworm
I agree. I'm sticking with what I said earlier. You can use a GPS for IFR flight. You can use a very large pepper mill if you want. You do not have to look out the window and map read as Keef suggests. (Not recommended in IMC)
You cannot use a GPS for approaches ie coming below 1000 feet above the highest object within 5 miles (10?).
However as I said earlier, in general, if you are doing a hold you are possibly in a situation that requires a working ADF whether or not you are using it at the time eg you are on airways or you are flying in Class A or D TMAs (see ANA?) or you are a BA pilot etc see (SOPs) etc.
As regards the discussion on how to keep in pratice, the only difference with an ADF versus VOR/DME or GPS is you don't have a miles read-out. This is only the same as a VOR with unavailable DME so you should be able to do this anyway.