ORION MK. V  I've tried many spam filter tools over the years. SpamSieve continues to remain the most reliable and effective, yet unobtrusive tool there is. Easy to uninstall or reinstall if there are issues as well.  
(Version 2.7.7)

DONPERREAULT  SpamSieve the best email filter/spam application on the market! Couldn't do email without it.  
(Version 2.7.7)

RON BELL  To set the record straight, my problem with the plugin not loading in Apple Mail under SpamSieve 2.7.7. has been fixed. It appears to have been associated with my use of Xslimmer, not with any fault in the plug-in. I should note that the developer responded to my inquiry in less than 15 minutes. Great program, great support.  
(Version 2.7.7)

RON BELL  SpamSieve is a terrific spam filter--i couldn't live without it! ... which is a problem, because version 2.7.7 generates the following message with Apple Mail:

"Mail has disabled the following plug-ins:

SpamSieve

Contact the makers of these plug-ins for versions that are compatible with Mail 4.1 and Message 4.1."  
(Version 2.7.7)

RBUGAJEWSKI  Greatest spam filter on earth!

SpamSieve is a plugin for a lot of different desktop mail clients. Most of them already have a spam filter, so whatÂ’s the point? SpamSieve is simply the best and most effective solution out there. I use this application with the built-in Mail.app since a couple of years and I have no more spam in my several inboxes.

IÂ’m a heavy mail user and itÂ’s astonishing how much time you can safe with this seemlesly smart and functional piece of software. And this for just a couple of bucks.  
(Version 2.7.6)

BEIGE  I just came back from vacation and had 7300 emails, 99.9% of it was spam. Spamsieve caught almost all of it (about 10 remained) with no false positives. Nuff said.   
(Version 2.7.6)

MOUSEE  I've been using this software for years and it is working in the background, doing a great job. It catches 99.9% of spam messages, and rarely sends a valid one to the spam box. Stability is great and so is the ease of use.

Upgrades have been coming when needed, and the developer is not charging for them unless a major one is released. Great policy, thanks!  
(Version 2.7.6)

RONL  Thanks Michael for keeping this updated.

Definitely the best spam filter out there for the Mac.

I recommend it to anyone that will listen.

Kudos for your excellent tech support also.

Easily 5 stars.

A must have!  
(Version 2.7.6)

KOMTOM  One of the best programs I ever had. It's like magic how SpamSieve filters out almost every Spam without making mistakes...  
(Version 2.7.5)

SEIKA7  SpamSieve has been updated to version 2.7.5. This is a free update that includes the following changes:

Made various accuracy improvements.

Fixed a problem where Apple Mail (running on pre-release versions of Mac OS X 10.6) could freeze at launch if you had a rule involving address book groups.

Rewrote the Setting up a Spam Filtering Drone instructions.

Added Why does the Spam mailbox appear empty when thereÂ’s a number beside it? to the frequently asked questions.

Updated the Automatically Deleting Old Spam Messages instructions to include Entourage.

The search fields are now scrollable.

The Apple Mail plug-in is better at detecting when SpamSieveÂ’s Dock icon is hidden.

Worked around a problem where Mail could crash if you had installed two copies of the SpamSieve plug-in at the same time.

Fixed a bug that could cause SpamSieve to freeze when applying a whitelist/blocklist rule involving certain regular expressions.

The crash reporter works better with pre-release versions of Mac OS X 10.6 (Snow Leopard).

Fixed a bug that could prevent SpamSieve from launching.

Updated the Dutch, Japanese, and Korean localizations.

http://c-command.com/blog/2009/07/29/spamsieve-275/  
(Version 2.7.5)