1. I noticed a large number of false positives, and Google provides a crappy interface for finding these, and a surprising lack of ability to customize how it handles spam.

2. Twice in six months, the POP service stopped responding for me for an hour (the Web service was still up).

Lately, I just route email to my POP server and to Gmail, using Gmail only when behind extremely obnoxious firewalls (you know who you are).

My issue w/ Spam Sieve is that Mail’s Spotlight integration includes its spam folder by default, whereas when using Mail’s native junk mail processing, it skips the junk folder unless explicitly told to search it.

The benefit is that I now have a lot of flexibility for routing mail, pushing some through the spam filter, and letting others skip it, depending on a variety of factors, such as recipient, subject, etc.

Combined w/ Spam Sieve’s integration w/ Growl to show you summaries of suspect spam, and its immense tweakability, and I’m a much happier camper.

There should be a “I’ll never buy anything from spam email” list that you can add your name to to save the spammers the effort.. Although unfortunately they’re not the most honourable of types.

My big gripe with spam is how butchered the web has become in terms of rel=nofollow crap everywhere in order to make google’s life easier.. Think the little “type in a number” stuff or a “mark as spam” button is a better solution. Google can just fix its algorithms if comment spam is getting good pagerank (or just ban searches for various *cough* enhancers, student l0ans etc etc)

Of course, you can also go with Google for Domains if you want to make things really cleanly.