The website for Square, Twitter cofounder Jack Dorsey's new startup, opened to the world yesterday and gave us more insight into what's ahead in the world of mobile payments.

With Square, users can attach a small card-swiping device to their gadgets (i.e. an iPhone) and accept credit card payments whereever they happen to be. It could come in very handy for small and medium-sized businesses, especially if it's robust enough for the enterprise. Users would get an electronic receipt like this one below:

Square is in a field that's quickly filling with competition. It just so happens that Square is coming along at a time when many tech experts and pundits are forecasting a sharp increase in interest in the realm of mobile transactions. Remember that Gartner report I cited recently? According to Gartner, mobile money transfer would be the No. 1 application by 2012, while mobile payments (what Square does) came in at No. 6.

Making spending money easier via mobile -- while decreasing our dependence on cash -- has some pluses and minuses, for sure. Pluses: convenience and accountability (your receipts are online). Minuses: potential security worries and slow adoption from the wary masses.

But what I like about an app like Square, though, is the potential it has to be used as a personal finance tool. I, like many people, use my debit card a lot for transactions. I hardly glance at my monthly account statements.

But if Square is able to track how often I visit the coffee shop across the street and tell me how much money I'm spending there over a period of time, that could start to influence my behavior. Maybe I'll stop buying so many $4 lattes and stick to plain ol' coffee for $1.60.

So, for many people who stink at tracking their personal spending, Square -- and similar apps -- could help structure the spending data we generate in our lives into meaningful formats for us to use in making decisions on how we spend. I'm looking forward to that.