Mint 13 is an LTS, potentially good for five years. To me, that means you can go
for four-plus years, then install another LTS a few months after it comes out.

I've heard too many horror stories from people who tried the simple upgrade path
in Ubuntu, so I have never upgraded, always done a re-install. I keep spare
partitions to test new releases, but tend to stay on one release for a long time
on my "production system."

I ran Ubuntu 10.10 for the full 18 months. (It fixed some problems in the 10.04
LTS on my system, otherwise I might have stuck with 10.04 for a couple of
years.) I was very annoyed that it expired a couple of weeks before 12.04 was
released.