Are purchases from the App store single or mulitple user licencing
You can install software from the MAS on multiple Macs. The only limitation in the EULA is that the software either is used by one person on multiple computers, or by multiple users on a single computer. So installing for multiple users on different computers would be a breach of the EULA (even though technically still possible if both computers are linked to the same Apple ID for purchases).

See http://www.apple.com/legal/itunes/us/terms.html

EDIT: I'll have to ammend my answer even though it was already accepted. While the above is true for commercial use, for personal, non-commercial use in one and the same household on the other hand the above EULA restriction is not true.