Having not ridden for over 10 years I can honestly say that the first week has really hurt my butt!
I don't think it has helped that I am using the same old bike that has been sitting in the rain for that length of time as well...
However with a few cheap fix me ups, I believe I have brought the bike up to a good enough standard where (and I hope) it does not break when I'm travelling at 20mph! However so far good, all limbs are still intact :)
This week I started at 3 miles per ride, working my way up to 12 miles.
My aim? To increase the mileage by 6 miles per week; and train my butt to ride for longer without being so sore... (Sort it out you people with the dirty minds!)