I think they're very cute. =] As to why, they're just something that accentuates and adds extra character to the face, with the added bonus of framing the smile. They may not always make a person more attractive. But at the very least, I've never seen dimples DETRACT from a guy's looks.
I've got them too though. Almost two sets, haha. One set is an inch directly below the outer corners of my mouth, between my mouth and my chin. I only have one cheek dimple though, on my right side. I have to be smiling pretty damn big or laughing really hard for them all to pop out at once though. I swear the cheek one is new, because I never noticed it until recently somehow. My only theory is that it hasn't always been there, haha.