To add to that, Exposure is your white-point adjustment and will clip highlights. Brightness will not cause clipping up to a point. Any value past 90 will compress highlights so much they are effectively clipped in most cases.
In Lightroom the Brightness and Contrast sliders are there for legacy reasons. The better tool for brightness and contrast adjustment is the tone curve.
An interesting point made by Steve Newbury (doing the Lightroom Demo) at Focus on Imaging was that the Brightness/Contrast in Lightroom is different to Photoshop and is actually being added to PS CS3.