While we patiently wait for OS X Lion to come out, here’s some preparation that you can start to think about. As you probably know Apple is going to make OS X Lion available as a download from the Apple App Store. We’ve posted before on how to install or transfer apps from the app store to multiple computers, you’ll be able to do the same with OS X Lion.
The difference is though, that Lion will be a big download. Some where north of 4G from most accounts.
So downloading it only more than one machine, while allowable from Apple could a) take you a long time and b) use a lot of your ISP bandwidth.
Download it once then make a bootable USB install disk to install on your other Mac.
Check out this post on OS X Daily, it covers exactly how to do this.
Update 22nd July
Make a bootable DVD for Lion installations
As well as the method outlined above another popular way of doing this is to make a bootable DVD to install Lion on other Macs. This in fact the method that I used last night to install on some Macs in our office.
I followed the instructions from this post on Cult of Mac here.