Are the key servers listed in the PGP documentation still active?

Yes, they are active.

And if so, what is the general opinion of using them?

It depends what you are trying to get to here? The keyservers were created as a way to implement out-of-band key distribution. They provide an easy way for you to get someone's key before initiating contact with this person. The key-servers do not do any key authentication, leaving the validity-checking up to the end user. It does leave a few things open, namely, anyone can see who has keys on the servers. But once a US-legal PGP does come out (RSN, I believe), it won't be as big a deal. I hope this helps. -derek