Katy Perry with John Mayer -- Is He Hittin' That Now???

John Mayer and Katy Perry were seen leaving the Chateau Marmont hotel in West Hollywood together last night ... damn you John Mayer.

It's unclear if the two were just hangin' out ... having dinner ... or doing something more salacious, but the sighting immediately ignited rumors that the two are some kind of an item.

It wouldn't be too shocking ... Mayer has been linked to all sorts of hot chicks ... from Jennifer Aniston, to Jennifer Love Hewitt, Jessica Simpson, Taylor Swift, Minka Kelly and more.