…you get this result:
You can also enter parameters, like so:
<lj-like buttons="google, facebook" />
…in case you want to select which type(s) of button to display. Presumably, buttons for other services may be available in the future.
I don't have a Facebook account, so when I view this in Firefox I only see the Google button. However, when I view this in Internet Explorer, I see both the Google and Facebook buttons – because it's in IE that my wife
EDIT: Now, in IE only, I see a third button which appears to be for a Russian social networking service.
EDIT: The Russian site is named Контакте, or "vkontakte" in non-Cyrillic characters. I mention that just in case anybody wants to use that as a parameter, to only allow a "like" button for that service:
<lj-like buttons="vkontakte" />
As near as I can tell, Facebook, Google, and ВКонтакте are the only services that LJ provides the "like" buttons for … so far.