I went from Tiger to Lion this past weekend. I popped in my Snow Leopard DVD and allowed it to install. That killed off 45 minutes. I then allowed the combo update to run. That murdered another half hour. Lastly I installed Lion using the app (which I saved off to USB before it had a chance to delete itself).
I actually have 2 usb sticks. One is for recovery or a new hard drive install. I made it by restoring InstallESD.dmg to an 8 gig stick before letting the Lion install app run. The other is for upgrading from Snow Leopard using Install OS X Lion.app and was made by copying the app to an 8 gig stick before allowing it to run. I didn't even bother with trying to upgrade directly from Tiger to Lion because I seem to remember there was a software update that had to run on Snow Leopard to make it upgrade properly and for that reason I didn't expect Leopard or Tiger to work.
If anybody has had luck skipping the combo upgrade of Snow Leopard before installing Lion, please let me know as it would save a half hour the next time I decide to upgrade which will be a while. All but our old G4 are running Lion at the moment. I'm pretty sure Apple is sick of pressing DVDs and will eventually push whatever secret sauce is required to SL and Leopard to allow direct upgrade to Lion. While upgrading directly to Lion from an OS older than SL is not a question of if but when, the answer is still not yet.
