Not sure about sourdough, but I do freeze quickbreads -- I've only kept them up to a month or month and a half before using them. They still tasted fine. I have froze regular homemade bread before, but it seemed a little more dried out once it was unthawed. I wrap quickbreads really well in saran wrap and then throw it in a ziploc freezer bag.
Quick breads should be frozen for 3 months or less. I do advise that you double wrap the loaves: first in foil or plastic wrap, then put into a heavy duty freezer zip bag or FoodSaver vacuum sealed to further protect against drying out and freezer burn. Breads in general can really dry out during freezer storage. Recently I froze a small loaf of Mexican cornbread and was totally bummed out at how crumbly it was after freezing. Had never frozen it before....so now I know. I guess frozen cornbread is only good for stuffing/dressing!
I used to freeze store bought bread all the time. My DH hates when it is frozen and he LOVES bread; he can always tell. Some of mine had been frozen for a while though--things tend to get lost in my freezer! Now I dont freeze it any more--only bagels. I will freeze quick breads though. Three months seems to be the consensus on them. MMM--that's right, there is that "best banana bread" recipe I wanted to try out of the BYC cookbook....Terri O
I usually only freeze bread if I'm planning on toasting it. You can hardly tell once it sees the broiler, especially once it's slathered in garlicy ricotta and mozzerella. I always preslice it and freeze it then package it for easy use. I find I don't use a loaf if its frozen solid. Also I freeze leftover french toast, yummmy. The DH loves to eat it instead of cereal in the morning. Easy! Again freeze individually and then package in a bag.