Maybe I'm just a complete sucker, but I get the impression U2 are really, you know, trying with their new album, No Line on the Horizon (out March 3 on Interscope). The cover is relatively mysterious. Bono's back in the makeup chair. And though first single "Get on Your Boots" suggests they're trying way too hard (as does the video...and the Grammy performance), I'll take that over the alternative (see: their last album). When you've been the biggest band in the world for a couple decades, simply trying at all goes a long way.The creepily ageless Irish crew (seriously, the Edge might look younger now than he did in the "Numb" video) will dig in for an unprecedented five-night run on  "The Late Show with David Letterman" starting March 2 (via AP). A Joaquin Phoenix rap cameo during U2 week is still being negotiated. Considering the just-announced White Stripes appearance set for "Late Night with Conan O'Brien"'s February 20 curtain call and this U2 spectacular (not to mention recent "SNL" spots from TV on the Radio and Fleet Foxes) we seem to be living in a mini late night musical guest golden age right about now.