Can I use the same Lion OS X license on a home and a work machine, or do I have to buy one for each?
Since you purchase it from the Mac app store the licensing is the same as other Mac App store purchases. I can't find the exact resource but I believe you can install it on up to 5 Macs.

Here is an article with some information about licensing in Lion. http://osxdaily.com/2011/06/07/single-purchase-of-lion-installs-on-all-macs/

Update: I found some clear language from Apple's Lion press release


  The Lion upgrade can be installed on all your authorized personal Macs