Well anyone who hates Jar Jar just isn't a true Star Wars fan as far as I'm concerned. I love him, he's one of my favourite characters.
But there is a reason he is in Star Wars other than for plot purposes. I think of myself as a Star Wars Scholar, so I'll enlighten the rest of you.
Star Wars is and always has been a movie about movies. It is an amalgam of genres, and that is precisely what George Lucas set out to do. Apart from the obvious ones like Science Fiction, Fantasy, Romance and Adventure, Lucas has inserted little bit of genre-mixing in other parts - the start of A New Hope is straight out of a Western, the extended musical seen in Jabba's Palace in ROTJ:SE was finally as lavish as the Musicals Lucas wanted to acknowledge, the detective story and lighting techniques of Attack of the Clones are conventional Film Noir, and every Episode is shot intentionally in a documentary-like format (no place names at the bottom of the screen, no inner-monologues, etc). Jar Jar is just another part of this - he is a homage to the classic Saturday morning cartoon characters we know and love. If it didn't look out of place we'd probably see Jar Jar opening a miniature umbrella to protect himself from a falling anvil. He falls over, he talks funny, his eyes pop out, let's face it he is a pure cartoon. So that is the real reason Jar Jar is in Star Wars - it is part of George Lucas' attempt to fit at least a passing reference to every film genre there has been into Star Wars, his movie about movies.