Obligatory what Eastleigh tells us post.
There's only one reason the Lib Dems managed to hold on in Eastleigh, and that's down to their organisation in the town. It certainly wasn't due to any love for the party whatsoever, or for how they've performed in coalition, merely that the voters narrowly preferred what they knew to either UKIP or the Tories. Which leads to
2. Having the right candidate
Who knows whether the Tories would have done better if they had someone other than Maria Hutchings as their candidate, but they couldn't have done much worse. Hutchings was fine for the 2010 election when the view of the nation was elsewhere, but out of her depth when in the spotlight. The Tory campaign was clearly terrified she was going to make even more of a mess of it than she already had with the schools comment, and when you have to tell the media she's essentially a volatile personality to explain why she's not giving any interviews, it reflects badly on you rather than her. Despite some snide remarks, I think John O'Farrell did a fine job as the Labour candidate; they were never going to win the seat, and his softly softly campaign was a better option than throwing everything at it and still not getting more than a 0.2% swing.
3. Stealing the policies of the insurgent party doesn't work
To all intents and purposes, the Tories and UKIP ran broadly identical campaigns: cap/stop immigration, have a vote on/get out of Europe, kill the first born, etc. The difference was the voters believed UKIP meant it, while anyone who thought immigration and Europe are pretty irrelevant to a place where neither has much of an impact had to choose between Labour and the Lib Dems. A leaflet on the day even had the Tories literally using UKIP's colours, to no obvious benefit. The Tory backbench belief is that if Cameron was a "real" Conservative he'd be able to win a majority. Rather, it suggests moving onto UKIP territory simply leads to further support for Farage's band and the disillusion of moderates. Why vote for the imitation when you can have the real thing?
4. But UKIP are still highly unlikely to win a seat
The rise in UKIP support can only be put down to one thing: protest. It can't be about immigration, which is coming down, unless there really are a lot of people terrified about Romanians and Bulgarians coming over next year, which I don't believe; it isn't about Europe, as not that many people ever place Europe as being a hugely important issue; and it's not about anything else, as UKIP don't have policies on anything else. Or rather they do, just that if people knew about them they wouldn't like them. There may be a kernel of truth in John Harris's observation that their bringing up of the loss of manufacturing in Eastleigh struck a nerve, yet this seems like a classic mid-term result rather than the emergence of a competitive fourth party.
5. Bombarding the electorate both works and pisses them off
For a by-election, a turnout of 52% is more than respectable. You also suspect though that the media and the parties would now do well to get out and stay out for the next couple of years.
6. The "Get Clegg" campaign by the right-wing press failed miserably
Apart from the hilarity of the Mail pretending to care about sexual harassment, the continued splashing on the party's woes over Lord Rennard seems to have had no impact whatsoever. It's rare that elections are won on anything other than local issues, and in this instance the circumstances of Huhne's resignation also had no impact, as the other by-elections triggered over expenses also proved.
7. Another hung parliament/just about workable Labour majority still looks most likely result come 2015
Eastleigh overall changes very little. What it does suggest is that the Lib Dems will fare better in their Tory marginals than they will in their Labour ones, which means they could still hold the balance of power come 2015. The Tories could conceivably win Eastleigh in 2015, as the Ashcroft polling shows, but it would take a gargantuan effort to judge by this performance. They seem to be keeping a lid on their anger for today, but the Tories as a party are in deep trouble.
8. Michael Gove is still a berk
Yes, Thatcher said she wasn't for turning. She still did, then denied she had ascribed to monetarism whatsoever.