I didn't make it over to the gulf coast side of the country, but I did spend over a month last year touring the Pacific side, and central Mexico. The roads were smooth, traffic courteous, and the people kind. All and all, it was a great experience that I look forward to enjoying again in the near future.
As for any kind of corruption by the officials at checkpoints, or drug violence, I never witnessed anything remotely close to what people hear about in the media, although we steered ourselves clear of major cities and only rode during the day, which is what we like to do no matter where we're touring. We were also consistently waved past the lineup of cars at every checkpoint we came across.
That's not to say corruption and violence doesn't exist there, it exists in some form just about anywhere you go, but even if it were a problem, who are they going to go after. A sweaty touring cyclist with very few belongings, or some tourists in a rental car?