I use emacs in the terminal, typically with many emacs instances running at once in different tabs. This is a perfect use case for emacsclient, but it has always had various glitches that have stopped me from using it. In particular, sometimes one client will "block" the other, preventing it from doing anything. It looks like things work better in emacs 24.4, but it still happens.
For instance, if I start two clients, and run
M-g M-g in one, to get the "Goto line" entry, the other client will be completely locked down until I quit in the first one.
I am using emacs 24.4 compiled without windowed support in Mac OS X 10.10 (in iTerm 2). I can reproduce it by starting
emacs --daemon -Q. If you want the exact emacs binary I am using, download Miniconda for OS X and run
conda install -c asmeurer emacs.