If you have Lightroom and are happy with it, then no, I see no reason why you should switch.
If you are looking for more library features, something I felt was missing with Lightroom, then yes, Aperture is very much worth a look at. There is a lot more to it than meets the eye.
I have both installed at home, but after some using, I decided that Bridge was just as effective as Lightroom is, with a less crowded interface, and Aperture is very slick for cataloging and doing mass editing in one swoop on many images, as well as having very nice auditioning tools for comparing images side by side.
It will be interesting to see if Aperture 2 has ironed out most of the issues found with 1 and 1.5.