Apple - How can I pair my Magic Trackpad with multiple Macs?

No, it can only be paired to one computer at at time according to Magic Trackpad Manual. You would need to un pair and then re pair it to another computer in order to use it on both computers.

Here's the extract from the manual:

After you pair your Apple Magic Trackpad with a Mac, you can pair it again with a different Mac. To do this, you first remove the existing pairing and then pair the trackpad again.

According to this answer, Magic Track Pads can be paired with multiple devices, just not, as you stated, at the same time.

As long as the track pad is not connected with another device, it will be pairable with an additional one. The trick is to make sure that it's not connected to the other device, since it will connect with the first paired device it sees.

If your machines in question are more than 33 feet apart (the range of bluetooth), you should be fine, but it never hurts to turn devices off when not using them and in-between pairings, just to be safe.

What about considering http://synergy-foss.org - an open source tool for sharing mouse and keyboard between multiple machines on one desk?

Support for Maverics is not ready yet :-( but it seems to be coming soon.