The D7000 is no more complex than a D90.
Its a better spec camera for many reasons and those you can check out on the web.
As far as focus issues with the D7000 I have found none, and niether have two friends who use the D7000 found any problems.
Its more about using a superb camera's focusing options correctly, you even have a focus compensation facility (what more can you ask for) Also auto focus on any camera should be treated with respect. Dependant on lighting, contrasts, and subject size and distance ect ect.
Know its limitations, use it properly, and you wont be dissapointed.
Tis a poor workman who blames his tools.
I loved my D90, and when upgrading to the D7000, I found an instant old friend. I love it, no regrets.