I've actually just started to look at this lens as a possible purchase. I have the Canon 50mm 1.4 which is super, stunning detail at around f8 and above on my 5D2. Not sure how much use I would get from the 85, but the extra distance would be nice as I like to isolate objects and pick out specific details. Anyway at around £270 ish (from Kerso) it seems like a good lens for the money.
Hmm, finding this thread potentially useful in the future, as looking to upgrade my 90mm f2.5 Tamron macro (also doubling as my portraiture / person lens) for a 180mm macro, leaving a hole in my toolbox. I certainly don't think I'd get the use out of the f1.2 for the price, but interesting to note chris321's comments on just how dark some situations are...

I love this lens. It gets me out of so many tricky situations on my 7d crop sensor not only for the length but also the sheer speed of it in low light. I just love it for portaits.
Out of interest, how does everyone find they get thee sharpest out of this lens? f1.8 is excellent but sometimes a tad soft.