No, i did a clean install on a testdrive (one of four ;-) on my 2008 macPro 8 core. Then drag and drop LP 7.2.3 from SL-disk, connect xsKey, et voilà: everything working. Then I installed LP9, with xsKey inserted, put in LP9 serial, everything perfect. Regarding LP8 i don't know, I'm not using it anymore.
Still not to much shure about Lion (and about Apples's startegy all in all...), sytem is getting too much prebuilt as far as I can see, but working with LP 9 and a lot of 3rd party plugins for the last 2 weeks without any problem.
The only issue concerning Lion : Firewire is causing sometimes little problems. I suspect the startup-routine of Lion is a bit different. Sometimes external HDD's are not recognized, sometimes my MOTU 896 is recognized to early and playing that high, unpleasant sound. Switching of and on again resolves the problem.
Best, Chrisrtian.