I am in two minds about this.
On the one hand, it is an audacious move. It will generate enormous media interest and public excitement over the next few days. It will also rally the Republican base and evangelical vote - Palin is anti-abortion, fiscally conservative, a member of the NRA, anti-gay marriage and religious - so McCain will be able to extend his appeal on the Right.
It is also a blatant attempt to appeal to the 'Hillaryites' who are still annoyed that their candidate didn't make it.
McCain interviewed her for the job and ultimately made the final decision. It is possible that he sees a steel glint in her eyes that we have yet to discover.
However, the decision also smacks of utter desperation.
Palin is unknown outside of her home state. She has no knowledge or experience of foreign policy and is mired in her own corruption scandal back at home.
I think the McCain camp also overestimates the hostility of female Clinton supporters towards Obama. They may be disgruntled for now, but it is quite another thing to switch sides and vote Republican in November. Will they be willing to vote for a woman even though she is anti-abortion? I just don't see how she appeals to them.
Palin will also find it difficult to hold her own against Joe Biden in the debates and on the stump. It will be clear from the start who is the more experienced campaigner and unlike Obama she has not been through the rigours of a Primary season.
However, the Obama camp has to be careful about the way they go after her. When it comes to the debates, Biden will have to tone down his combative and blustering nature. He must also avoid being seen as patronising and belittling. It will be a fine line.
My guess is Palin will probably surprise us and turn out to be quite a good campaigner. If I was McCain I would let her work on shoring up the Republican base, while I concentrated on the Independents. The media and women's groups will also love it initially. But, I think over the next few weeks it will become quite clear who has the stronger ticket. The ethics cloud hanging over her head may come back to haunt her and her extremist policy stances will do very little to win over Independents and Hillaryites.
The decision also tells us something very interesting about McCain's character. If he were to be elected, he would be in charge. There would be none of the co-Presidency we have seen under Bush and Cheney. If Mitt Romney or Tom Ridge had been chosen, for instance, then they would have established their own centres of power. But does anyone seriously think Palin is going to stand up to McCain? Offer him policy advice? The answer is no. Unlike the Obama/Biden ticket, this ticket doesn't look like one ready to govern now.
She will turn out to be mere window dressing. In time, Americans will see right through it.