I'll start the ball rolling. Only one - so far.

Gunmaker: W.J. Jeffrey
Appox manuacture date: As a guess 1900's to 1920
Calibre: .450 No. 2 Jeffrey
New or pre-owned: Definitely pre-owned
Condition when bought: Worn blueing, stock refinished by someone, on-face, tight, one bore a little worn but both in reasonable shape
Did you have it checked over: Absolutely, dropped into a gunsmith, who actually had also extensively checked over the same rifle for the seller when he purchased it
Any problems subsequently: Minor, foreend screws came out when first shot and filling in front sight was dislodged as well
Ammo regulated: First load in it regulated well enough to satisfy me. Was high but that was more my sight picture I was using. But still need to shoot a lot more loads to see just what it does
Other: N/a
Commercial interests: I run an independent of any maker double rifle forum - NitroExpress.com