I have to admit that I'm a fan of software based anti-spam applications versus appliance. I've used Network Associates and Symantecs software programs to block and stop spam from reaching Exchange email servers. The Barracuda spam filter is an appliance that I've installed on numerous occasions and have found that the installation is always less complicated than those applications that need to be installed directly on an email server.
For those of you that have the pleasure of having to install applications on Exchange box, you know you have to take that deep breadth and get a little psyched because as you know, anything could go wrong.
With an appliance there is much less pressure in regards of worrying that you'll lose a sever in the process. Just rack and configure ip addressing and your off. With some tweaks, the appliance is doing it's job. The one thing I absolutely do not like about this spam appliance in particular, and there could be others that don't suffer from the same lack of feature, is that it has no integration at all with Active Directory.