After spending the holidays together, Katy Perry and John Mayer are setting tongues wagging about just how hot and heavy their relaysh is getting.

The pair were decidedly dressed down for a recent dinner date, showing that they're getting pretty comfortable with one another (maybe too comfortable!), and their friends are spilling that they're getting pretty serious. And we all thought it wouldn't last!

"John is surprised at just how cool and smart she is," a friend of Mayer told Us Weekly. Another pal added, "John has proved he's matured and learned from his mistakes ... Katy is blown away."

If anyone can tame a bad boy, it's the former Mrs. Russell Brand, right? One pal dished, "They are seriously in love and exclusive."

Congrats to these two! Hope they work it out -- and that Johnnyboy can keep quiet about it.

Watch the Katy Perry 'Wide Awake' Video