To be honest, if you are unsure about how much use you will get from the above lens, you should seriously consider the non L equivalent - the Canon 100mm F2.8 USM macro lens at practically half the price.
I have owned the non L version for a long time (5 years) and the quality is probably not far off the L glass version except it does not have the IS of course - the non L version, surprisingly, is not much lighter than the L IS version.
They can be used for portraits and other things as well, they are more versatile than you would think - you just have to use your imagination.
In 2005 when I got my first digital slr I took a few pics on a day out using just that lens. The pics arent great as I was just learning the camera and the lens, but to give you an idea of its uses, here is a gallery I created at the time:
http://www.pbase.com/lindabuckell/scotney_castle
I now use it exclusively for macro and I also have the Canon 60mm macro which is also a very fine lens indeed and worth considering.
Hope the above is of some use to you.
Linda