In reply to Jules:
Oooh, that's made me think.
When sport climbing, if you are moving left/right above a bolt (rather than straight up) then you should clip the krab to the rope with the back of the gate to the direction you are moving. This reduces the (admittedly very small) chance that the rope will unclip itself from the krab.
This being the case you should probably have the bolt-krab facing the same way, as otherwse when the system is pulled tight there is a higher chance that this will be loaded across the gate rather than the back of the krab.
On the other hand I might have made that up.
For the record I was told this by some very, very good sport climbers, so it isn't that the uber-hardcore oppose the gates.
The above applies to sport routes, it seems even less (though still marginally) relevant to trad routes.