It's been an interesting few days, Lion installs failing left right and center, or so it appears.
I've just upgraded 7 machines to Lion, three 13" MBP's (2x2010 & 1x2011), a couple of iMacs (2009/10) and two 15" i& MBP's (2011)
All 7 installations worked first time and at no time was any installation or data at risk from a failure (mine or otherwise)
Take 1 external drive (big enough to hold the internal) and (using CCC or SD) clone your internal drive to it, reboot to the external and test the clone. Download and install Lion to the external drive you are currently booted from, after the installation reboot to the (now Lion) external.
Play with that long enough to find out and decide what to do with anything that doesn't work (in my case Quicken, but I knew and had exported the data to See Finance previously)
When happy with your Lion install clone it back to the internal, you are finished now. The external (which is a copy of your internal now) makes an excellent start point for a CCC or SD clone tat you can use as a backup drive.
Note that while testing Lion from your clone that it will be slow, because it's on an external drive, this is temporary.
In conclusion, all installations work perfectly, Lion is as fast or faster on each machine than SL was.