I've been very lucky and very UNlucky.
Two lines I have for definite back to the late 1500's. They just happened to come from places that have very well preserved and recorded records.
another line, I've got stuck on my G g grandfather, b.1850.
My Dad's surname, Porrett, was very easy to trace back to the 1850's, but there are almost exlusively williams and george's in the families previous to then so untangling them is proving quite difficult, and all the wives seem to appear out of thin air!
definitely is interesting, I've found myself doing it for my boyfriend (his is v interesting as they're Barons and Admirals and things), friends, and even two random customers my dad had in his garage!
Should probably start charging.. :p