How to synchronize settings between multiple computers?

See http://devnet.jetbrains.net/docs/DOC-1143 . You need to use one account.

One account per instance. Therefore to sync 2 applications I'll need 2 accounts, otherwise it won't sync between.
Also, you cannot login from 2 machines with account.

To make things clean:
I have only once license to PyCharm and only one account on jetbrains server.
However I have multiple computers and I'm using PyCharm on all of them.
I want to syncrhnoze IDE settings (keymap, menu items etc) automatically among all computers
Is it possible?

Yes, Configuration Server Plugin is exactly for this, you can use the same license and the same account on all your computers to synchronize settings.

Odd, but I cannot login while there is an instance of PyCharm running on another mac (already connected).
Looks like the server refuses simultaneous connections.

It's by design, concurrent use is not permitted by the license agreement:

(b) Licensee may not:
(iii) allow the use of the same License Key by multiple Authorized Users, on multiple instances of License Server, on multiple Clients or on different operating systems at a time. The Software may contain a feature preventing concurrent use of the same License Key by multiple Authorized Users, on multiple instances of License Server, on multiple Clients or on different operating systems at a time.

It's likely the server does not support simulatneous connections with the same account.