or less 
DH is in charge of washing his own towel and I am sure he never puts it in the wash more often than once every 2 or 3 months...
DS's goes in about once every 2 months (but it barely touches him as he likes to run around naked pretending to be a train driver straight after his bath, which dries him quite effectively).
I usually wash mine about every month but have realised that I haven't washed it since coming home from hospital with DD, who is now 5 weeks...in my defence, there is one HECK of a lot of other washing to do and it just won't ever fit in the machine....
We do wash out clothes (!) and sheets once a week. And I do the kitchen hand towel every week or two - it gets quite grubby and also fits in the machine with another wash easily.
But are we grim and disgusting when it comes to bath towels? How often do normal people wash bath towels?