Drew,
As for rarely bothering to look for it, that is the current situation.
I'm hoping that the long-awaited "notification overhaul" will include an option to receive an email notification when someone likes (or unlikes) a message of yours.
Right now the likes have too little visibility on the web as well. Which is one of the reasons I've proposed "has likes" (among others) as a message filter to go with the existing date range filter. But the more complete solution for the web is that a like on one of your messages (or other content) should be in your online list of notifications, however that is presented.
Shal
Shal Farley