Mark Kleiman links to the AP story on John McCain, which has more detail on what, exactly, McCain is supposed to have done wrong.
In late 1999, McCain twice wrote letters to the Federal Communications Commission on behalf of Florida-based Paxson Communications — which had paid Iseman as its lobbyist — urging quick consideration of a proposal to buy a television station license in Pittsburgh. At the time, Paxson's chief executive, Lowell W. "Bud" Paxson, also was a major contributor to McCain's 2000 presidential campaign. McCain did not urge the FCC commissioners to approve the proposal, but he asked for speedy consideration of the deal, which was pending from two years earlier. In an unusual response, then-FCC Chairman William Kennard complained that McCain's request "comes at a sensitive time in the deliberative process" and "could have procedural and substantive impacts on the commission's deliberations and, thus, on the due process rights of the parties." McCain wrote the letters after he received more than $20,000 in contributions from Paxson executives and lobbyists. Paxson also lent McCain his company's jet at least four times during 1999 for campaign travel.
Kleiman asks "Is it routine for a Senator from Arizona to pressure regulatory agencies on behalf of companies based in Florida?"
Fox News has these details, and is making it sound like this is not a big deal, because the senator did not press for an outcome, but only a speedy resolution. But regulatory uncertainty is very costly for firms; just getting your case jumped to the head of the line could be a pretty valuable special favor. It doesn't cost the rest of us much, of course--unless we happen to work for the company whose case was delayed while everyone dropped everything to deal with the senator's request.
That said, I don't have a good sense of how much impact this sort of thing actually has, and I suspect it's (sadly) rather common.