Personally, I think this guy-liner stint is due to Bono hanging out with BJ Armstrong from Green Day while they were making The Saints Are Coming.
The bowler hat and umbrella are definitely a Clockwork Orange reference, and probably something U2 should stay away from, given that other bands went that route recently (Gnarles Barkley for one).
I don't hate the look for Bono, but I'm not yet a huge fan. It would take a character change, as a lot of posters suggested, and some different attire to really pull it off.
My take on his shades has always been the following:
1) Yes, his eyes are sensitive, but mainly they get red and inflamed from drinking red wine and probably smoking. The glasses mask the redness and puffiness along with dimming the light.
2) He's getting older, and had stretched himself pretty thin in the last few yesra. Those shades do a good job of hiding the bags under his eyes and help him look a little younger.
3) They're iconic, they're kinda cool, and it helped him establish an image. He let the pope wear them, and it was a huge photo-op.
The eye-liner might help with part of 1) and certainly a lot of 2), but he'll have difficulty 'owning' the look if he's ditching 3).