Tamiflu is already given to people like poultry workers who have to destory infected chicken flocks or health care workers (if they can afford it, that is). There's still no good evidence on whether it's actually protecting them yet since transmission is still rare anyway.

Hypothetically speaking, if H5N1 went pandemic, I'm sure that it would develop resistance to Tamiflu fairly quickly. And the more people who took it, the faster it would happen because the more the virus would be exposed to it. It's the same argument people make about overusing antibiotics, but influenza virus can mutate much faster and more radically than most bacteria.

I would add that the possibility that a flu strain can quickly develop resistance wouldn't necessarily be an argument for not stocking Tamiflu, at least at the community level. You can still potentially save a lot of lives before resistance develops. Then again, considering how much it costs, maybe ensuring more basic preparedness would be better money spent. <shrug>