Even if you had successful upgrades in the past,
chances are slim with 12.04 because almost everything has changed since
10.04, including the boot process, window manager, desktop environment and
many of the services that run behind the scenes.

It is worth a try, but backup and don't count on it too much. That being
said, the folks at Canonical believe in upgrades and work hard to ensure
they work for most users. The profile of a typical LTS user works in your
favour as they tend to stick more with OTB setups and run low risk
environments with few changes. The ones who tend to have problems are those
who customise and use outside sources.