Info about concurrent sequential scans

Hello,

at Prato PgDay in 2007 I remember hearing in a speech about a (then
yet to come) "seqscan piggyback" feature, allowing concurrent
sequential scans to use the same disk reads. I've now googled for info
about this feature, but I found nothing conclusive (e.g. [1], [2] -
which I don't know where is linked).

So I'd like to know:

is this feature currently implemented (I'm specifically interested in PG 8.3)?
Is there any prerequisite needed to benefit from it (config setting,
query characteristic, etc.)?
Is there any feedback showing the feature kicking in (e.g. an explain
analyze output, log, etc.)?

Thank you very much.

-- Daniele

[1] http://wordpress.metro.cx/2008/02/24/postgresql-83/
[2] http://www.postgresql.org/about/featuredetail/feature.26