Some people find the sound to be blisteringly annoying, while others find it pleasant. It has been argued that it's a pointless, inane and stupid activity, but I would have to disagree. Otis Redding, Carter Burwell, Billy Joel, Axl Rose and Andy Griffith would all back me up on this.
Whistling. I'm a whistler. I whistle whilst I'm working, when I'm in the shower, and anytime the mood strikes me. I've often been whistling for a while before I notice I'm doing it - the tune in my head self-actualizes. If I'm going to sing (and stand the fuck back) I often whistle pitch before I start. When singing, I might whistle instrumental accompaniment. I definitely whistle better than I sing, and it's more brain-engaging than my iPod. I've also had my lips longer than my iPod, so there's a continuity factor, too.
Aside from the aforementioned tracks (all of which are definitely in my limited repertoire), I have a number of other tunes I can annoy people with and that seem to crop up in my internal whistle jukebox on a fairly regular rotation. There's the obligatory Cole Porter (this linked version, with Harry Connick Jr. is the lullaby I sing to my kids because it's something I know all the words to) and Sinatra, but there there's also some slightly more common things - things I just can't get off of:
The Witches of Eastwick Main Titles: John Williams. Kind of a cheat, since everything by John Williams is imminently whistleable - the Indiana Jones theme is always a favorite, too.
White Rabbit - Jefferson Airplane;
Sweet Home Chicago - Robert Johnson;
The Ballad of Ira Hayes - Johnny Cash (just the chorus, really)
Crazy Train - Ozzy;
Han Solo - MC Chris;
Behind Blue Eyes - The Who (though often in my head, this becomes the Bill Hicks "Dustbin in Shaftesbury.")
The Lazy Song - Bruno Mars;
Smoke Two Joints & Santeria - both by Sublime, the former of which can be a problem if I'm bored in a public / parental setting and someone recognizes it;
The Doctor Who Theme music (relatively modern era) - because I am an obsessed person;
Vivaldi's La Primavera; and I do always think of Nigel Kennedy playing it, hence the link.
There's plenty of other music that runs through my head, but I can't whistle it all, and I've subjected you to enough links now, I think. Are you a whistler or a hummer? A public singer? Have you music in your heart and wish to confess it in an ill-noticed public forum?