Not a big fan of the Joel on Software but this is an amazing article... ...I used to be one of those "house programmers" too!
Oh well, at least its expected that an employee will move around a bit.
If you're going to be stuck doing something shitty, it's well worth the effort to try and make it less shitty.
Trust me, even when your bosses are onside, in-house programming is a PITA. You're better off talking to your boss about how the product you made on your own is better than some of their in-house stuff, and that he/she should buy it.
Of course, that's got it's own set of problems.
I currently work as an in house guy and it really is a PITA.