Cable stretch?!
 

After some time, I finally got the bike I'm building together. I got the derailleurs shifting smoothly, took the bike off of the stand and had a joyous trip around the block to make sure it was indeed shifting properly and that the brakes were nice and tight. All was right with the bike, so I put it back up on the stand, wrapped up the handlebars and crimped the cable ends. I went to blockbuster, watched half a movie and then decided to play around with the bike. Now the chain is rubbing on the front derailleur and the rear cassette is noisey and shifts poorly.

I guess the obvious answer would be cable stretch. How long is it going to take for these cables to stretch out completely? I'm tired of adjusting things.

the first stretch is going to be the bulk of it, but I would say it takes more than a day.

Thats why barrel adjusters are provided on most bikes. It is possible your cable tension has changed because you are getting some slippage on the termination bolts.
When I replace my cables I usually only have to make very minor adjustments on the barrel adjusters then the cables don't need to be adjusted for months. Cable stretch was a problem in the old days before new Steel.