
I thought Obi-Wan's astromech droid on his Aersprite snubfighter in Ep2 was R4-P17 or something like that? But generally, I also thought the "R2D2" designation was for the entire line of that particular variant of the droid, compared to R2D1, R2D3, etc. but since we never see two identical R2 units interact and named we don't know if that is canon.
Artoo's amazing code breaking skills came from the fact he never got his memory wiped, so accumulated huge amounts of experience and nous compared to the standard R2 units - notice at the end of Ep3 Organa gets C3PO wiped but not R2, which is why the speaking member of the pair doesn't recognise anyone or anywhere in Ep4-6, but the wee fella does. He basically lives through the entire, tumultuous events of the last days of the Republic, the Clone Wars and the Rebellion and is the real hero of the movie series... not bad for a rolling dustbin with pr0n plastered on the inside of his dome!
@Allan Dyer
I believe the Israeli Defence Force put a tender out for battlefield laser anti-missile defences last year, and are looking at the US Army version of the vehicle mounted laser.
http://www.spacewar.com/news/laser-04r.html
Even Paris recognises droid from a ring found in the desert.