Spam as a tax on public participation in open source projects
One of the things that has struck me lately is that spam has become an implicit tax on publicly participating in various open source projects. The mechanisms of this are fairly simple: if you have a sufficiently popular open source project, the spammers are sitting there mining the project mailing lists and their web spinoffs for email addresses and then spamming the heck out of them. There's probably also spammers mining web-based bug trackers too, where bug trackers expose this information.
(Actually, this is probably a simplification. Based on my personal experience, it seems more likely that there are people harvesting fresh 'hot' addresses from these mailing lists and then selling them to spammers, primarily advance fee fraud spammers.)
Open source projects are particularly susceptible to this because they still make heavy use of public mailing lists and so reveal your email address when you take part in them. 'Taking part' can be quite minor; just briefly dipping into the conversation at the wrong time can be enough to get your address harvested.
This is a tax because spam degrades the usefulness of an email address. The more spam an address gets, the more that will be missed by whatever automated anti-spam defenses the address has and thus the more you'll have to deal with personally; the end stage is the address becomes dead.
The obvious workaround is to use a revocable email address whenever you need to participate in public (and expect to revoke it periodically and switch to a new one). One of the problems with this is that it damages the long-term usefulness of old mailing list messages (and email addresses in VCS commit logs and so on), since many of the address in them will no longer be valid.
PS: possibly I am over-generalizing from my experience, but I don't really think so. Alternately, perhaps regular participants develop a thick skin for spam (or you have to have a thick skin for spam in order to be a regular participant).