I didn't know that gabapentin was the generic for neurotin, but it's a med that my pain mgmt doc switched me to, currently at 300mg 2x a day, but said the ceiling on it was 3600mg, so 2400mg while it sounds like a lot might not be too bad.
As far as functioning altering side-effects go, I haven't noticed any clouding of the brain, dizziness, drowsiness or weakness. It's actually made me feel like I might be able to return to the work force after far too long of an absence.
Granted that's just my experience with it, everyone will be different and I do have an exceptionally high tolerance to medications and even alcohol. (Never been a cheap drunk

bright side is I'm too poor to be an alcoholic though

) but then again the goal of the medication should be to kill the pain and not the brain. If it's doing both, I generally ask for something else or a change in dose until a balance can be found, it's never fun playing pill bottle roulette or pharmacy grab bags but I like to think of it as a treasure hunt.