I got this lens lately and I love it. Not only it is good for taking macro photos but it works very well as a prime lens for anything else. Its autofocus isn't that slow as I was able to take some action shots.
More information about that lens is available at http://www.sigma-photo.com/lenses/lenses_all_details.asp?id=3253&navigator=5

Here is a photo of a lady bug:
http://www.megapixelworld.com/photography/showphoto.php?photo=2083

I am leaving to the south of France on Tuesday and I hope to get macro photos of flowers or insects as it is almost like summer there compared to London.

It must be great lens for portraits too.Enjoy the new world you could see through the macro lens :)

Another photo taken with that lens:
http://www.megapixelworld.com/photography/showphoto.php?photo=2102

I was able to add a macro converter Canon 500D I used to attach to the Canon Pro90IS as its diameter was 58cm like the Sigma macro. It works well with it but it is hard to have everything sharp.

Very nice photo!when i got the macro i also used to put the Kenko macro filter on the lens,but i finally believe that it doesn't needed,the quality of the lens is very good even if i crop the photo at 100%,thus i'm able to take a nice enlargement.
When i put on the filter the quality comes down,did you notice that with your lens and macro converter?maybe you have not this problem because Canon macro converter is better than Kenko

I think I am also losing quality when I add the converter but it is hard to tell. I would have to do some tests using a tripod to be sure.