What do you use or recommend for an enterprise anti-virus solution? Please include your good and bad experiences; they're valuable information for others considering solutions.
Please be specific about versions, some products have improved or not over the years.
Consider the term enterprise anti-virus to mean a company-wide or location-wide managed anti-virus solution that mostly consists of a central server that administers the updates and communications with the anti-virus clients.
This is not limited to Windows environments only.
Note: made into community wiki since there is not a definitive answer. Just looking for a collection of experiences to help others make a more informed buying decision.