My initial thoughts are that I'm happy with picture quality - to my eyes it seems sharp throughout the range and has pleasing bokeh.
How it compares to the tamron - can't say! But I do think the difference has been overstated - remember the Tamron got 8.5 and the sigma 8.0 out of 10 in a subjective test, which is hardly worht mentioning.
What IS worth mentioning is how much I love the near-silent autofocus that the HSM offers. It brought a "WOW!" reaction from me.
Overall, I'm definitely happy with my purchase - I'm hoping I'm allowed to take it in to the Football Stadium tonight (with a small monopod) - conditions of entry to ban "professional photographic equipment", but surely a pentax doesn't fall into that category
P.S. It was actually camerawarehouse (not dcw) that had it for $949:
http://www.camera-warehouse.com.au/ but I rang up Paxtons (who have more of a physical presence and long-standing reputation), and they were happy to price match for me.