Regarding spam filtering, you actually can get as good if not better than Google's. I use bogofilter, the main issue though is that when you first start using it will be quite bad at filtering, you will have to continue to train it.
I actually use sendmail with bogofilter-milter.pl script (there is also bogom program with does similar thing) as opposed to usual way of running it with procmail, it essentially does the filtering at the moment it is being sent to you and rejects spam right on the spot. The advantage of it is that sender will get notification that spam was not delivered, also many spammers might drop you from their lists when they can't deliver spam.
Using another method (catch-all with a blacklist) I also get better filtering than gmail can offer. Much less sophisticated and a little more trouble, but much more effective.
I actually use sendmail with bogofilter-milter.pl script (there is also bogom program with does similar thing) as opposed to usual way of running it with procmail, it essentially does the filtering at the moment it is being sent to you and rejects spam right on the spot. The advantage of it is that sender will get notification that spam was not delivered, also many spammers might drop you from their lists when they can't deliver spam.