I liked how @garybernhardt had specific rails shortcuts in vim for his Selecta script. As a fan of CtrlP + Ag, I did not want to switch, so I came up with the following which works well.
map <leader>gv :CtrlP app/views<cr> map <leader>ga :CtrlP app/assets<cr> map <leader>gc :CtrlP app/controllers<cr> map <leader>gw :CtrlP app/workers<cr> map <leader>gm :CtrlP app/models<cr> map <leader>gl :CtrlP lib<cr> map <leader>gs :CtrlP spec<cr>
The pattern should be obvious. One mistake I initially made was using:
map <leader>gl :CtrlP<cr>lib/
This ends up just entering lib/ for you in the search and does not explicitly limit the search to the lib directory. This is noticeably slower since each keystroke is a wasted search. Also, with a small directory name like lib, it is easy to have invalid fuzzy matches. The CtrlP + directory and then enter keeps the search focused on the specified directory only.