Which distro of linux?

[Jonti]

Once stable, do they modify the upgrade; ie. the 6.06lts one, or leave it be?

It's the finished product. It gets bug fixes and the like. By default, LTS releases will only be upgraded to the next LTS release. You can get paid technical support for three years on the desktop and five years on the server LTS releases.

The next LTS Ubuntu is likely to be 8.04, so, not the next one