Aside from the 1980's when a lot of big names were caught cheating, a lot of people are viewing this as the darkest day in the sport and a negative thing. I see a flip side: The argument against track and field's integrity is that the dopers always win and that doesn't make sense anymore if these people are being caught. Gay and Powell are arguably two of the most successful and high-profile sprinters of all time and the sport isn't afraid to let them go at the expense of keeping the sport clean.
So with the testing the sport getting better with the biological passport, I think it's just a matter of time before the sport will be clean. Athletes like Lance Armstrong were able to get away with doping because they didn't test out of season, but now an athlete has to submit to a drug test any time of the year wherever they are.
To keep having improvement in keeping the sport clean, there needs to be a steady stream of funding behind that cause. Part of the reason the dopers have often been one step ahead of the testers is that the funding hasn't always been there for USADA and WADA.
As for the next stage of performance enhancement, I think it might be gene manipulation because doping has traditionally followed scientific progress. The reason any of these performance enhancement drugs exist in the first place is because they were initially developed in the medical community. Similarly, the scientific community is looking at ways to manipulate genes. Now when athletes tap into that, that could be a losing battle. How do you test within someone's DNA?