it holds its own against Horizon, III, Aleph and the big boys of integrated library systems.

Not even close - I've been keeping an eye on Koha and Evergreen, but they're missing a *lot* of features that our commercial ILS has . It costs an awful lot of money to run (and even more to buy in the first place), but until they support things like EDI, serials, and proper acquisition management it'll be very difficult to sell them to big libraries, even with the obvious cost savings. Koha has got a lot better lately, but it *still* doesn't support LoC classmark as far as I know :(

Anything that reduces costs for some libraries, and raises the bar for the commercial vendors has to be a good thing, though.