Tony Blair also took an unusually long summer break, and Michael Howard has been pretty quiet too, but the difference is that neither of those two men intends to lead his party through another general election campaign.
And neither Blair nor Howard has been accused of letting personal problems get in the way of the job they had to do, whereas Kennedy had a few very bad patches when the air was thick with rumours of heavy drinking.
If he looked a touch bleary-eyed when The Independent on Sunday called into his office, it was because he was under the influence of a different stimulant, writing this week's big speech. For any opposition party leader, the speech to the annual party conference is one of the most demanding engagements, and Kennedy is not going to spare himself any punishment in Blackpool in the next few days. He is making two set-piece speeches and doing a Q&A session with delegates.
So where has he been all summer? At home, is the answer. A boundary change in northern Scotland means that, for the first time since he was elected to the Commons at the age of 23, his constituency has expanded to take in his home town, Lochaber, so when he is at home, he is also in his constituency. And he now has a five-month-old son, Donald.
"I had a two-week family holiday, which people might think is not unreasonable," he said. "I have spent most of the time in my constituency. My seat is now only slightly smaller than Northern Ireland and that takes a bit of time to get around."
His long sojourn in the Highlands set off more talk in the Westminster gossip mill, which he hopes to bury in Blackpool this week. It was being suggested that after 22 years in the Commons, Kennedy had lost the appetite to carry on and that his party had lost its direction.
The idea that the party is suffering some sort of identity crisis is just "tosh", he said. "When domestic politics reasserts itself, what we will see is a much more focused attack on the Liberal Democrats from the Government, for the perfectly obvious reason that we are the principal contenders, not the Conservatives," he said.
That is a bit of a wild claim on the face of it. The Conservatives have 197 MPs to 62 Liberal Democrats. But Kennedy pointed to the inroads Liberal Democrats have made in northern cities where the Tory party has been voted almost out of existence. And those young voters who came over to the Lib Dems because of Iraq or tuition fees will stick around, he predicted. "We did disproportionately well among young voters. Did they agree with us over Iraq? Yes. Did they agree about tuition fees? Yes. And about other issues too. I think it's wrong to say, 'Well, it was only a snapshot of the issues at a given time'.
"People are coming round to voting for the Liberal Democrats' position in total, partly on the issues of the day, partly on the individuals involved - and not just the leader - and partly because they agree with our general approach to matters political."
It is only in an unguarded moment, when the talk turns to the Tory leadership election, that Kennedy hints at trouble in his own ranks. "And I think I've got problems!" he exclaimed with feeling.
He then made elliptical remarks about what he calls the "almost theological problem" that a party's MPs might support one leader, while the majority of its members prefer another. Kennedy's popularity is almost certainly higher within the rank and file. He is so sure that the Tories are on the way down that he sometimes talks as if almost the whole country is made up of potential Lib Dem voters.
"It's an essentially liberal, democratic society. Readers of The Independent on Sunday know what that means: it's tolerant, it's fair-minded. What you haven't got yet is a translation of that into support for the party that calls itself Liberal Democrat. But this year has been fundamental in that contest for the hearts and souls of the people."Reuse content