I would offer the exact opposite assessment than Danielle. Certainly, there is no question that skill matters, and that you must understand how to use any tool before you can use it effectively. On the flip side, it is absolutely false that better technology can't improve your own capability, whether you are highly skilled or only moderately skilled. Its not just one or the other, neither skill or the tool matter solely. But if you are using a 9-pt system and move to a 19-pt system, or using a 19-pt system and move to a 61-pt system, the improvements in the system will most certainly raise the bar.
When I went from a Canon 450D with a 9-pt AF system, which I knew how to use at a moderate level, to the Canon 7D with its 19-pt AF system, all of my photography that relied on AF improved considerably. Once I had more points to work with, my skill quickly improved as well...my problem, as I found out, wasn't simply that I sucked at using the AF system of my camera...it was that the AF system of my camera sucked. I've been using my 7D for about 9 months now, and I'd consider myself an expert at using the AF system. After two years working with the 450D I simply couldn't do with it what I knew was possible with an AF system, and I stopped bothering to push myself to learn more after a while.
So no, its not just about skill...the tool and its capabilities most definitely matter. In fact, a better, more capable tool can help you improve your skill by removing boundaries and limitations that could quite possibly be holding you back.
To offer a basic comparison of the D7000 and 7D AF systems. The D7000 certainly has more points, rolling in at a total of 39. However only 9 of those 39 are cross-type, where as every point in the 7D system is cross type. The D7000's cross type points are only present in the center 9-point 3x3 block, where as the 7D's cross type points fill the entire AF area. Single-line sensors are only capable of detecting phase in a single plane, and as such they will have trouble with certain types of subjects. Cross-type sensors are capable of detecting phase in both the horizontal and vertical plane. A diagonal cross-type sensor (often called a high-precision cross-type sensor) is capable of detecting phase better than a standard cross-type sensor, and are thus the most effective.
The 7D's AF system with a full spread of 19 all cross-type AF points is its strength. It may have fewer points than the D7000, but each if its points are more capable than the 30 single-line points in the D7000. For what its worth, Canon's tracking logic seems to be pretty good in the 7D. Its not top of the line...its certainly been surpassed by the 1D IV, 1D X/5D III, and D4/D800 AF systems now, but its pretty good and fairly configurable to meet differing needs. Another strength of the 7D AF system over the D7000 system is the dynamic point and zone selection options. You can select a smaller area of any given point for "spot AF" for greater single-point precision, select the four surrounding points of the selected point for "expansion AF" for better single-point tracking, and you can select any one of a variety of "zone AF" regions where multiple points, but not all 19 points, will be used for less predictable AF. Nikons 9, 11, and 21 point modes are not as effective or configurable as the 7D's.
Nikon has had an edge in AF systems for nearly four years, however starting with the advent of the 7D, Canon started clawing back the title. The 7D's AF system brought some new capabilities to the table that hadn't been offered before. They took those new capabilities the the limit with their new 61-pt Reticular AF system in the 1D X and 5D III. If your looking for top-grade AF, Canon certainly won't disappoint. How long Canon might maintain the AF crown, particularly in terms of configurability of the AF system will have to be seen. I'm sure the competition will put up a fight, and things will probably normalize in a few years (depending on whats been patented, I guess). If you do get a 7D, it certainly won't disappoint.
