One of the examples of web apps that handle user data right is Wesabe. Their attitude to data is spelled out in their Data Bill of Rights:

and practically in ability to export data in CSV or XML formats.

Their ‘competitor’ is mint.com (far more popular in the US and not in any way related to this MINT), which provides similar functionality to wesabe. At a glance the main difference is in their focus – wesabe is more community oriented money management tool, mint.com is more about how many ways you can benefit from money management. That said, I use wesabe without the community dimension, I am interested in understanding and managing my spending better. (Also, I believe mint.com doesn’t handle UK bank statements, only US ones.)

Investigating Mint.com’s approach to user data, I came across this thread in their support forum. It’s from 2007, so not a news flash, what caugh my eye was the user reaction:

It took a couple of weeks for mint.com to sort that out and all is well.

Why use Mint section has a use case spend less eating out and a testimonial:

Trying to rein in his spending, Sean Hsieh began using Mint.com to track his expenses this summer. [He] was shocked to learn he was spending $800 to $1,000 a month dining out.
—Orange County Register

The obvious point about this is that user autonomy increases with understanding own behaviour, which happens with observation and analysis of own data.

Knowing how much you’re spending is the first step to managing your money. Knowing any other things about your behaviour is the first step to pursuing what you want. This is why this MINT is pushing for liberation of customer data, focusing on purchase history as that is fairly consistent (relative to other customer data companies might collect) and straightforward to do.