Usability Testing - Worth The Investment?

I don't like buzzwords. In fact I'd almost go so far as to say that I loathe them. Of course I do use them - it's really hard not to. For the last 7 years or so I've been subscribed to Jakob Nielsen's newsletter. I missed a few issues over the years due to moving emails around (I have a tendency of doing that!), but I've always found his reports to be thought provoking. We're currently working on a couple of things to improve the company website and other public interfaces ie. control panels, order forms etc., As a result of this work one of the things that I have been thinking a lot about is usability. While it maybe a nice idea to have an accessible and usable website my motivations are much simpler. If we can make things more usable, then it will be easier for people to buy stuff, so we should, hopefully, get an increase in sales. Even if we don't get a direct increase in sales our costs should be lower. Why? The following example illustrates what I mean. Up until about 2 months ago we used to get a lot of phonecalls from people who wanted to pay for their hosting / domain renewals online. We've been offering the facility to do this for ages, so I was a bit confused as to the volume of phonecalls. Eventually the proverbial penny dropped: The link for credit card and Laser payments was simply too subtle for people to notice it. We knew where it was, but our poor clients didn't. Solving the problem was very easy - I just got our designer to do up a couple of obvious buttons and we integrated them into the billing system. The number of calls dropped dramatically! The addition of a simple graphic made it all that much easier for people to do things. So I'm currently thinking about how we can combine usability with gorgeous design while also focussing on our site's key purpose - sales. If anyone has experience of usability testing and reports I'd love to hear from them. PS: I blame IQ Content's post about AIB's interface for this. It really got me thinking!