I did it on a system that has undergone these violent steps:
1) Fresh install Mint 6
2) Dist-upgrade to Mint 7 - saw some system crash issues, which disappeared along with updates
3) Backed up the whole system using tar (https://help.ubuntu.com/community/BackupYourSystem/TAR
4) Dist upgrade to Mint 8 - didn't like it (some RC, I recall...)
5) Restored the whole system from the tar archive
6) Dist-upgrade to Mint 8 after the official x64 release
Been a happy camper again
This was on a T61 Thinkpad. I actually saw a power usage drop after the last upgrade to Helena (-2 watts), using PowerTop.
I come from a Ubuntu background, I started with Ubuntu in 2006. Back then a dist-upgrade was a big no-no for me, but with recent releases, it's a viable option. Especially since I'm lazy in a way and don't like to reinstall all my apps.
EDIT: Oh, and I used the command line option to upgrade, as described in the blog post.