Simon,
I like this lens a lot too.
I think you do need to carry a 32 mm extension tube with it always. It's 2.5 m minimum focussing distance is a bit long, and the tube will help you get that extra bit closer.
One thing to remember using this lens is that even without tubes you need to apply an exposure compensation of 0.5 to 0.6 stop when used at distances shorter than 3.5 - 3 m.
With the 32 mm tube (with matches the lens's built-in 31 mm extension very nicely) and the lens fully extended you need to add 1 full stop.
F/5.6 is a bit on the dark side, so a tripod is a "must" (when isn't it?).
Or at the very least you will have to find some other suitable support.
You can "get away" with "handholding", but trust me: compare images shot handheld with those taken fom a tripod, and you'll see what a waste of a good lens handholding is.
But when i a push... ;-)
Stopping down even further makes matters worse, of course. But (like Ruben said) you do not need to: you do not increase depth of field by much, and the image quality does not improve. So i genreally only stop this lens down when i run out of shutterspeeds.