SpamTitan's performance at filtering spam is nearly perfect. There are not much spam mails coming through and if it does, they are not clearly "spam". Also, the support is great - normally you get an answer after a few hours and a working solution for you on the same day.
It's hard to find such a great product at this price! Give SpamTitan a try. If you use the On-Premise version check the status of URIBL. In most cases, you use a high volume DNS which leads in blocked request at URIBL (which is used by SpamTitan to check Links). In this case, you have to buy a separate "datafeed" service at URIBL (volume).
SpamTitan filter's about every spam mail which is sent to our mailboxes. Employees don't complain about spam mail anymore. SpamTitan works fine for mailboxes and public folders (mail address based solution). A lot better than VIPRE.