Cheers guys
. I haven't got round to bugs - yet! Dod, there's no cropping at all - this lens gets close enough. I tried this lens and the Canon 100mm macro and imho this is much better. The only downside is that the autofocus can hunt a lot, but the manual focus collar is very good to use and fine tune. All these were taken with manual focus.
Sigm EX build quality is very good and you get a hood which takes 77mm filters (making the use of a polariser easy) and a substantial carry case. The Canon costs £100 more and you have to buy a hood.