I work in an industry obsessed with novelty, so it must be the contrarian in me that likes to see software last a long, long time.
OdeToCode.com started almost 10 years ago. Internally there were 2 different applications running the site, and over the years we made tweaks and added features, but most of the code was the same code from 10 years ago.
A couple weekends past I sat down to fix some performance problems and, in a fit of short-sightedness, ended up rewriting everything (except for the database) from scratch. The result is a leaner, meaner, single application that will be easier to move to an environment with more headroom, like Windows Azure.
I hope I don't have to do that again for a long, long time.