A. Lot. Two words. Simples!
Maybe I'm a bit of a grammar and spelling Nazi. I know its easy to make errors on Facebook, forums etc. I don't continuously correct other peoples spelling and its easy to make errors when you are typing quickly. I usually post via my phone so am using a predictive text app that can sometimes make some howlers. But a lot is not difficult to get right. It's not long or complicated, and doesn't even need and kind of memory aide to remember (anyone recall one coffee two sugars, or big elephants can always understand small elephants). And SO MANY people seem to think it's one word??