I have to admit thay i've always just changed them once a year (as someone who plays the bass alot, 15 hrs a week or so), but i was curious if anyone has good suggestion for really knowing. With EB i can always tell because of the sound but on DB it's much harder because the change happens so slowly. I've been suspicous my strings are a bit dead know, but i'd hate to throw on a new set and not have them sound any better.

playing on D'addario hybrids, FYI

I am playing on D'Addario Hybrids as well. They are my favorite steel string. Dark, and they sound pretty good arco IMO. DB strings last a long time. I change mine when I start to loose pitch definition. The intonation starts to waver. Depends on how you play, and how much you play.

how would you evaluate that? I thought those intonation problems were just me . . .

My strings need to go when they seem to be noticably harder to play in tune, they feel stiffer, the tone is either too muffled or too strident - dependent on the type of string, sometimes they will need tuning too often. I think the pitch problem comes from damage by overstretching.

I am talking about the open strings not sounding focused. The pitch starts to waver.