If I move over to iCloud can I still sync two Macs (calendar and address book) as I am doing now with MobileMe? Or does iCloud only sync iOS devices?
Yes as long as the Macs are all running Lion, there currently isn't any check that enforces the "you need an iOS device to get iCloud started".
Just head on over to https://www.icloud.com and follow the instructions. The guides and tutorials that are linked as part of the signup process are fantastic and answer all of the questions you have about the service.
If you are not ready to start, you can see what the setup looks like on a Mac (or PC or iOS device) from How to set up iCloud.
This link http://www.macworld.com/article/162953/2011/10/icloud_syncing.html has the information you're looking for. Note that there is requirement on the version of OS X of your Macs.