I was taught that funner is not a word, but after reading a debate about it I came to the conclusion that fun has transformed into an adjective in the modern English language, and it is therefore acceptable. It's just difficult to hear it because of years of rejecting it, but I can get used to it (I don't think there's anything inherently wrong sounding about it). Just don't use "more" or "most" with "-er" or "-est" (they already imply it), that still really irks me.