In reply to whenry:
I've got a collection of assorted bladders and mostly use Platypus. Both of them have started leaking around where the hose attaches and have been sent back to be replaced, so they do have a good warranty.
I've also used Salomon, Ultimate, North Face and bits of Camelbak hose fittings. I've not used the bladder that came in the Osprey pack I've got or the Camelbak one my sister gave me. My wife has a DaKine one, which seems very flimsy, but has held up so far. Anyway, they've all seemed like much of a muchness to me, although I like the baffle in the Camelbak that helps keep it flat and reduce sloshing - even if the Ultimate one I had 25 years ago did it first!
Have to say I've never used a 3l one - but I have taken 2x 2l ones (not full!) on some long hot walks before.