Maybe eval'ing to the repl is almost a tic of mine. But as a contrived example, (range 100000) is instantaneous in a clojure repl in the terminal, and interminably slow in cider (emacs package for clojure). There's also SO questions like this[1], and I've personally come across it a lot as well. Anytime lines get long emacs grinds to a halt.
Geiser might just be adding a lot more newlines by default. There is a setting in CIDER to pretty print everything, which alleviates the issue. The core problem is emacs is terrible at displaying/wrapping/navigating/editing long lines.
[1]: http://emacs.stackexchange.com/questions/598/how-do-i-preven...