I second everything already said. I started riding again a month ago (after buying my bike from on here) and my first ride was 0.7mi and my legs ached. I've built it up bit by bit over the weeks and yesterday (Sunday) I rode 12.6mi on a new route I planned out and it was a little tough at times (mainly because I live in the damn hills north of Manchester!) but overall I felt great afterwards.
Next I think I'll have to ask the missus to drop me off somewhere with the bike as I'm running out of long distance "loops" to start/finish at home without having to tackle a monster hill :-/
And as matisko said, enjoy it :-)