In theory, yes; if the invention is "known or used by others in this country [the US]" prior to the date of the invention by the patenting inventor, it counts as prior art.

http://www.law.cornell.edu/uscode/usc_sec_35_00000102----000...

It's tricky, though, because that's the invention date, not the filing date, and the "inventor" could lie about the date of the invention. The safest approach is to publish my ideas in print in a foreign country, ideally in a small print run in a language spoken by nobody at Intellectual Ventures, and then wait a year before posting to the list.

Prior art does not have to include a reduction to practice; conception of the invention is sufficient. Lore has it that Charles Hall's waterbed patent was narrowed substantially by a reference to Stranger in a Strange Land, which described waterbeds.

Serious question, not meant to infer anything --

but if you used a centralized server for your blog, wouldn't the date/time stamp of that server provide the same information as a mail server would?

In other words: wouldn't that file/database entry timestamp (ie: wordpress' time -- just an example/name of a blog not necessarily available at that time) serve the same purpose?

Yes — but if an evil person were running a blog like that, they could write posts about other people's inventions and put fake old dates on them. They could also fake the timestamps added by their mail server, but not the timestamps added by the mail servers of their subscribers. So the timestamp wouldn't have as much legal weight.