Also, because this is commonly confused, drivers that use multiple threads (like the recent N64 work or the Voodoo emulation) are a completely different thing from -mt. You do not need -mt to get the driver-threading benefits.
thanks to both.
@Arbee: I got confused by this because the first time I used N64 rewritten driver my system hardlocked and forced me to turn off: I blamed the mt (not being set at all in the ini), but it might have been a series of others factors, given I had ~10 different programs running together at that time and that it never happened anymore...