Running 10.5.8 on my MacBook Air and it works great and have done so for the three last years - My next MacBook Air will be delivered with Lion
On my iMac I have two partitions and runs both 10.6.8 and 10.7.1..
On my Mac Mini I runs 10.7.1..
Hackintoshes runs 10.6.7, 10.6.8 and 10.7.1.
The Hackintoshes have two boot partitions so I can tweak on one partition at a time and boot from the other if something goes wrong as it does "most" of the time...
And I have even an external disk or two with a cloned partition and a plain vanilla installation in spare so I can connect and boot from when something goes really wrong.
In some cases when it is the bootloader that have bugs I can boot via the USB stick bootloader (bootable Lion install).
Most of the times you get stuck are due to one changed text string in a file or a combination of kexts, or bugs in a new release of a bootloader - so it is needed to have alternate boot options.
My advice are as follows:
Make a bootable USB stick with Lion installer and a bootloader that can boot any 10.6.x and 10.7.x systems, and have one spare disk or USB stick with a 100% plain vanilla 10.7.x installation - plain vanilla here means that you only install 10.7.x and absolutely non others like kexts or running MultiBeast or installing a bootloader of any type.
With the bootable Lion install USB stick you can run diskutility and also run terminal and fix most problems if you know how to use it, or boot from the 100% plain vanilla installation (on most hardware that supports Lion) and use GUI tools like MultiBeast, KextBeast, Chameleon Wizard, DSDT editor etc.. to "repair" your ordinary installation.