Well, taking the question at it's face value (and I believe intent), rather than every possible permutation and possible meaning under the sun, there are a few things holding me back.
Firstly, my ambition. I want to shoot adventure type photography and motorsport. I've successfully shot both, and enjoy it immensely. However, the gigs are severely limited in number for someone living where I do. If I was willing to change my ambition and shoot portraits or landscapes, I live in, and on the door step of, one of Australia's most scenic areas. But thats not what I want to shoot, so, I mope and kick the dirt.
My gear definetly doesnt hold me back. I have every lens I can possibly need (save for the 500 F4, which *might* happen), and then some, I have multiple bodies, and then some, I have studio setups, flashes, backdrops and more. Heck, I'd even be so bold as to say I have the skills to use them also. Thats not to say I''m not looking at some nice D3s bodies......
My time is a limiter. I have a full time job, with lots of recalls, and, being separated from my wife means on my few days off, I have my boy. (He doesnt pose well, I tried taking his photo). I also have a new lady in my life, so the time I get that I dont have my boy or dont have to work means I spend it with her. (She is taking her first steps into photography though....
).
And so, to 'advance' my photography, I need to make the step into the unknown. Find a niche. A niche that can fit into my current life style... and I have one such niche in the wings.... Just need some more gear....
Oh, and thanks to the original poster, this has been a little bit of a cathartic post for me