Mostly 2008 on 9-3ss with an extra sprinkling of America.
They first came out around 2006 after Saab had to chuck a vast amount of money (somewhere around $140 million) on development so that Cadillac could break into the European market, I have no idea what GM were thinking of with this strategy as if they'd have invested the same amount of money in Saab R&D and marketing for Saab it would have made sense to increase Saab sales rather than bringing yet another brand to market in Europe. This is the major reason that I believe GM will eventually die, they had something like 15 brands at one point all competing with one another in very similar market segments with very similar models. Compare that to successful auto makers who generally have one or two major brands in each market with some differentiation between them in one way or another.
Personally, I wouldn't buy a BLS either as the prices are not that good compared to a 9-3 and they have enough different parts that I think servicing and repairs could be very difficult, I'd expect that the software needed to get a Tech-II to talk to them would be different than that of a 9-3 too. At least, before I considered one it would have to be very very cheap to be an option.