This is a minor consideration but one that is relevant for commercial sites. There is an expectation from non-technical users that a website starts with www so when they don't see that they might not think of a domain as a website. Whilst it may seem silly to those of us that know how things work I have come across this attitude frequently with family, friends and non-technical colleagues and these people are likely to represent the vast majority of your customers.
Additionally, a lot of software such as email, world processors, social networking clients &c. will automagically recognise a domain name starting with www as a hyperlink and make it active - with a naked, or non-www, domain you will need to add the http:// for the software to make it active. Being able to click a link instead of having to copy-paste into a browser could make the difference between a customer visiting your site or going to your competitor.