Let the handicapping begin. Amid the downward economy — and a general consensus that things are going to get worse before they get better — predictions are starting to surface about which Web 2.0 start-ups may go by the wayside due to a lack of revenue. Rafe Needleman, editor of CNET’s Webware, chimes in with a list of what he calls 11 troubled Web companies, including Pandora, Twitter, Second Life and Skype. While all of these Web sites are popular, Needleman says, that may not be enough to sustain them amid the economic meltdown. In a related item, Twitter CEO Jack Dorsey tells Newsweek that other companies will suffer from the downturn, but not Twitter. “It’s going to be painful,”  he said. “There’s going to be a lot of fallout.”