Let's see...

• Character sets I can't read count as undeciperable, right? 306MB and counting. 166MB of that is GB2312 alone. (This is since August 27, 2002.) The various ks_c_ charsets between them account for another 60MB.
• Stuff either doesn't specify what charset it's in or that's theoretically in character sets I can potentially read (mainly, UTF8, which I unfortunately can't filter because some people in the open-source community write English messages in it in preference to ASCII or Latin-1, for no discernible reason), but the subject line contains either long strings of non-alphanumeric characters, or nothing but alphanumeric characters, probably also counts as undecipherable. Another 141MB. A handful of these have long strings of punctuation in the subject, but most of them are Unicode messages written in a non-Latin writing system. 141MB since September 2003 when I wrote the rule.
• That virus from a while back, "See the attached file for details", 235MB.
• Assorted miscellany my filters didn't catch, 166MB (between 2004 April 23 and December 6; I start a new bin for this periodically so I can calculate the impact per-day and see how much it's increasing).
• I did get one CPAN bug report once... for some reason I filed that under nnml:perl.* rather than under nnml:spam.*, go figure.

The unfiltered stuff (which lands in my inbox and gets shifted manually) is what annoys me most, and I'm continually looking for ways to reduce it, without getting false positives. (My experiments with Bayesian filtering were a wash; after training ifile on my entire very large corpus of mail, I found that I had to continually go through the whole spam bin for false positives. With the system I use now, I don't go through the filtered ones, only the unfiltered ones that land in my inbox.)

Some of the kinds of spam that land in my inbox include the following:

• Messages with an enigmatic or vague subject line (that looks like a Markov chain or random dictionary words) and no content -- absolutely nothing in the body at all, no HTML part, no attachment, no nothing. I seem to get a fair amount of this, and I'm confused as to what possible reason the spammers could have for sending it.
• 419s. I haven't found a solid way to detect them (without false positives) yet.
• Phony giveaways
• Adverts for warez
• pornography
• Adverts for medical products that do not, in fact, exist: ways to reverse the aging process, cures for cancer, and the like
• Spam written in Latin characters, but in a language I don't read. Spanish predominates in this category, but I've seen German, French, and I think Italian. If I get any Portuguese, I probably mistake it for Spanish.
• Spam written using non-Latin characters (but without specifying the charset as such, either because it's not specified at all or because it's unicode) that slips past the filter rule for non-alphanumeric subject lines by throwing in alphanumeric characters in a few spots.
• Various prescription meds adverts that slip past my filtering rules. Most of them seem to slip past, even though I've tried to be clever with my regular expressions. I write stuff like "^Subject.*[Vv].?[Ii1l|].?[Aa@].?[Gg].?[Rr].?[Aa@]" but they still find other ways to say it and slip past. I think they use lookalike Unicode characters. Did I mention that Unicode is a plague and a nuissance? Yeah.
• Sundry other nonsense and junk.

However, even the stuff that gets filtered is a significant annoyance, because of the bandwidth it uses. I'm on 33.6 dialup here, so retrieving my mail takes a few minutes; when most of what I'm retrieving is unsolicited bulkmail, it's annoying to have to wait for that.