I will leave to Andrew Sullivan, who has the advantage of being an actual Englishman, the live-blogging duties for the Brown-Cameron-Clegg debate. But from having watched and written about a zillion of these things in American politics (eg here and here and here and here), let me make two quick points while seeing the BBCAmerica live stream:
1. This really is different from a US presidential debate, because (based on my half hour's exposure) it really is about policies and arguments. Or if you prefer, slogans -- but in any case, the speakers are mainly addressing each other, rather than (as is often sane for US candidates) performing in sequential solos to the camera. The timeless -- and accurate -- lore of US political debates is that they're not about policies. They are about the public's getting a sense of the person and deciding how they feel about him or her. That may be good and it may be bad, but it's how things are. The Brits so far may not really be advancing the overall level of public knowledge, but they're acting as if policy differences are the point of the exchange, rather than scoring one of the "You're no Jack Kennedy" "There you go again"-type dramatic moments on which US debates have often turned.
2. Gordon Brown is really, really terrible as a public figure. Every time he wags his head scoldingly "No, No" when the opponents are speaking, he must lose another 500 votes. No policy judgment here. Just saying that -- based on this sample, plus these past few days' "bigot" disaster -- this is someone with neither aptitude nor (apparently) training as a TV-era public figure. The more that the general election becomes "presidential," the harder it is to imagine that people will choose to have him around for a few more years as the main figure to listen to in the news.
That is all. Over to Andrew.
UPDATE: Brown's final words, which were also the final words of the debate, were a quite attention-getting "a week from now, I will be out of office" (in not exactly that form). It was an emotional roll of the dice but -- I say based on zero knowledge of the dynamics of the British electorate -- likely at best to add a note of pathos rather than to draw much support.