I don't know about the worst mistake, but the best one was when i bought Mosier's old set for 50k and sold it for 250k or 350k, i'm not entirely sure o/.
Then i ended up putting all my money in TP and VIP when Crux and Fee sold them for TC.
It was cool as long as it lasted, but after all it was pretty crappy investment. TP/VIP boards sucked. Having cool big avvy's and sigs was awesome tho.