[exim] Using + to specify delivery folders in addresses

I've been toying with the idea of using the "+" character to denote a folder
separator for local addresses, so that I could use addresses like
eli+exim-users@??? and have email delivered to the eli@???
account under the "exim-users" folder (if it existed).

I'm wondering if people have this implemented, and if so how well it works
(as in, does it get exploited regularly, or cause other problems or
configuration issues/complexities), as well as wondering if anyone may
provide configuration pieces showing how they've implemented this (as well
as where it's implemented, such as in ACLs or routing - or both).

Thanks in advance,

Eli.