What do you think of off-leash dog parks? Are they safe places to let dogs run and play?
Sorry, but I'm not a fan of off-leash dog parks at all, simply because I don't know the dogs that will be there and how well balanced they are. While it's invaluable experience for a young dog to be "thrown in" with a pack of well balanced dogs, there's usually no way of knowing in a dog park which dogs are balanced and which are not. The last thing your dog needs is a run-up encounter with an ill-tempered Chow Chow or a neurotic border collie mix. This is not the type of experience you want for your dog in the off-leash park.
If you're absolutely certain that every dog in there is compatible with yours--if you know the dogs and their owners--then by all means, let your dog have some fun playing like a dog. But if it's a larger or more public area, I say don't risk it.
I've found that most dog park advocates tend to be a bit more idealistic and lenient-minded than I am. It sounds like a wonderful thing for a dog to run au natural, but unless you know who's in the playground gang, I'd urge you to err toward being an overprotective parent. There are better and safer ways to socialize your dog. Form play groups among your friends or dog school buddies. Find a responsibly run doggy day care. Take your dog everywhere with you and expose him to the world. And use a leash unless you're absolutely certain that circumstances are safe for an off-leash romp.