Pros
You'll learn a lot in you (probably short) time here. You DO get thrown into the deep end from Day One, but chances are you'll come out knowing how to save yourself from drowning, NOT how to be a great swimmer. Catch my drift? There are genuinely awesome people here and you'll get a chance to try lots of different things, but the pace is so fast (one might say artificially so), you'll feel like you're not getting anything done.
Cons
Incompetent, rage-prone management, psycho clients, cliquey work environment. In PR, you're only as good as tomorrow's headline. That's the nature of the business. But here, management consistently over-promises to clients and when results don't immediately materialize, junior people are "motivated" through screaming and subtle threats ("we're going to lose the contract!"). It's treatment I've never received in a workplace before or since. You'll notice a core group of people who don't seem to do anything except gossip loudly in the halls and have long lunches on the patio. These activities appear to be key to the agency's operations. Try to ingratiate yourself with those people. It's probably the only way you'll last. It's a small company but forget about getting to know all your coworkers. This place is a revolving door and people quit/are fired/hired at an alarming rate. Also, get used to screaming matches, both behind closed doors and out in the open for the whole staff to see. Get used to being on the receiving end of some of that abuse, no matter what you have (or haven't) done. Go outside for a quick cry, if you must. Others have. You're never going to get anything done. Just accept that. Look, there's "fast paced" and then there's just poor management. If your priorities shift on you several times a day, if you have so much on your plate that you never make progress on anything, if you're always the last person to know despite repeated requests to be a part of planning...well, which case do YOU think it is?