I'm probably in the "Coldplay bugs me" camp, though I don't really voice that opinion on the board too much, but the few times that I have, it's not as disrespectful as some other posters. That said, I'll try to explain where these somewhat irrational emotions originate from.
On their own, Coldplay are rather harmless to me. They write catchy, tasteful, melodic songs. A number of their songs actually rub me rather well. What gets to me is when they are compared to U2, because in my eyes the very act of doing so is insulting my favourite band. It reduces U2 to a formula, to a stereotype, to a particular sound, when to me they are much much more, and what makes them special to me is precisely that they're more.
Are Coldplay talented? Undoubtedly? Are they, in my strongly felt opinion, within a 1000 mile talking distance of U2? Not in the slightest. Their music is highly derivative post-punk (although more so of Echo and the Bunnymen and Radiohead than U2). Now of course, everyone has their influences, but to me, Coldplay are more their influences than they are anything of their own. I dont think that's true at all of U2 or Radiohead.
They appropriate the most superficial and listener-friendly elements of each of these bands and present them in a mild, harmless, easy-to-stomach incarnation - the ringing, minimalistic guitars, the keyboard ambience, etc. Their musical diversity is threadbare compared to U2. Could you imagine Coldplay writing songs like Electric Co, Refugee, Exit, God Part 2, Acrobat, The Wanderer, Numb, Do You Feel Loved, In a Little While, or even Love and Peace? Part of what makes U2 greater than good is that they have challenged their fanbase radically at various points in their career. Same with Radiohead. To call Viva La Vida challenging in the same respect as Achtung Baby or even TUF is, I think, simply unfair.
What stands out in even starker contrast is the lyrical content of Coldplay's songs. Their lyrics are utter dross. They are often nothing pretending to be something profound. I dont get that sense with Bono's lyrics (until ATYCLB) at all. Right from Boy, the words MEAN things. The songs are ABOUT things. And they're very often good, and sometimes downright great. Twilight? Promenade? A Sort of Homecoming? Red Hill Mining Town? Angel of Harlem? Until the End of the World? Please? Have Chris Martin's lyrics come close to matching these heights? Have they ever even promised to do so? Not to me. They write songs that represent a general sense of angst with no specific object (unlike U2's, which have their angst rooted in specific events, like the loss of a mother, events in the world, etc).
So that's my problem with Coldplay. On their own merits I don't really care about them, they're harmless lads who write good pop tunes that I hum along to at times. But when people compare them with U2, it greatly undermines the brilliance of U2's musical, lyrical, and artistic achievements. It's the equivalent to me of saying "U2 are a post-punk band with ringing guitars, 4/4 bass, angsty-sounding lyrics, with a shitload of record sales", which I think is a ridiculous straw man characterization of U2. It's like being a Michael Jordan fan and hearing that some guy who has a 30 PPG in the regular season is being called "the next Jordan". Simply does not recognize the greatness of his achievements. To that extent, I find the Arcade Fire comparison much more palatable - to me, they actually DO threaten greatness, and promise to have many of the qualities that make a great band. If the history books are written with any sanity, Coldplay will go down as an immensely popular band with a highly derivative sound. But greatness? It will be a sad day based on evidence received thus far.
