I haven't done any crazy amounts of miles in one go yet, but I'm in my second week of pretending to ditch my car. I'm planning on taking my car off the road (boyfriend's car is better anyways) for the summer, but we get some crazy lake effect snow around here (buffalo) and I can't imagine getting rid of the car completely. I still plan on exercising my badassity by riding in the rain (got some fenders and a nice biking rain shell), but I don't know if I can do the snow. We'll see, I'm going to try and keep my car off the road for as long as I can stand! I might attempt some bike snow tires, I'm just afraid of ice, or if we get 2 feet of snow overnight, etc.
Anyways, I made it through all of last week and today with just my bike! Work is M-F about 2.3mi each way. I even rode to the grocery store today and filled up the new pannier bags that I sewed for myself :) They aren't as good as a bike trailer, but they'll suffice for my bi-weekly trips, a lot of the bigger items come from BJ's once a month and for now that will require a car. Even better, they keep me from buying too much or getting anything on impulse since I know I might run out of space!
As far as big distances go, I promised my mom I'd do Ride for Roswell with her on the 30 mile route so I'm trying to work up to that, I just did an extra 5.5 mi ride in this gorgeous weather! I'm loving biking (especially over paying $4/gal for gas!) and it's only getting easier as I go farther and get better.