Perusing the Amazon.com sales stats for the DSLR category and thought I'd share a few VERY UNSCIENTIFIC observations that I think may shed a little light on market share, at least as far as Amazon buyers, which I realize is very specific sampling. Nikon entry levels holds the #1, #2, and #4 sales spots, with the T3i nestled at #3. Nikon has been working very hard to outpace Canon on the entry level front, and it seesm to be paying off. This can have consequences down the road for lens sells and "prosumer" sales, but probably not anything significant for a few years. On the flipside, in the top 10 are five more Canon cameras and one more Nikon, all entry level EXCEPT for the 7d at #10. The 5d Mark II appears not long after, with the D300s and the D700 lagging behind considerably (likely due to the D700's production shortage over the summer). In sum, Canon is still strong in its Amazon marketshare, but is clearly vulnerable at the entry level, the bread and butter of sales. I think we may see a new APS-C sensor very soon and it will be telling if Canon follows the same 7d-Rebel-60d progression or if they shake it up.
Canon made a wise decision by re-wrapping the 18mp sensor of the 7d multiple times, taking full advantage of the r&d and reducing long-term production costs. The 5d Mark II sensor has only appeared in one body. While I realize they are distinctly different lines with different consumers, I think it's likely we will see the next full frame sensor used in multiple bodies, possibly even a more financially accessible body. If the progression from the 7d to the T2i to the 60d was a financial success for Canon, it's likely we'll see the 1Ds IV before a 5d successor, and may even get a $1700 full-frame thrown in the mix prior to the release of the 5d III.