Pros
It's fun! There are parties to attend constantly and you get the benefits of lots of concerts, sports tickets, etc for free! There are also generally many opportunities for advancement, especially if you are willing to move to a new area and if you are interested in taking on a new job. Once you are in the door, your benefits only increase and the opportunities become more abundant. There are also different branches and a number of training activities, so almost whatever your job, you will have an opportunity to go away for training on that position and related software.
Cons
It's publicly traded so there is a lot of red tape. Plus, you have the FCC to watch out for if you are on air. Sometimes you can end up in a market that doesn't have the best management. If the management skills at your particular market are less than adequate, that can really decrease your satisfaction and functionality. I think many people who have worked for Clear Channel and gave a bad review probably just were in a bad market. But Clear Channel is set for success, so if you aren't happy in your market, I'd suggest relocating to another before writing off Clear Channel altogether.