I had to dig out some 5-year-old Scala source a few weeks ago. Honestly it wasn't hard to port - there's a deprecation cycle and the compiler warns you about anything that's deprecated, all the fixes were pretty mechanical. I think a statically-typed language makes backwards compatibility changes much less dangerous than they otherwise are.
I dug up some 15 year old cweb code the other day. Not only did it just compile on my first try, but it then succeeded in being among the fastest pieces of code I've ever run. :)
Even better, I weaved it into a pdf to read, and I was actually able to understand what was going on. The idioms were ancient, but that is another matter.
