While I've known of their existence for years, I have never bothered to try to receive an ARRL bulletin of any kind. The ARRL sends bulletins of all kinds, from Keplerian elements ('keps') for satellites to propagation data for HF radio signals.
After hearing some fast code practice on 160m last night, I decided I would try to pull down tonight's 'digital bulletin'. A huge swath of information on propagation greeted me. The information, of course, can be downloaded at the ARRL website, and can be received via email. I know a lot of hams who forward these messages incessantly, I'm not sure who they're trying to benefit. People who are interested in this arcane data will seek it out.
That said, receiving the bulletin via PSK31 was interesting, and I could certainly see the Keplerian data being useful. I might try to update predict using data received from an ARRL bulletin one of these days just so I could say I did it.