I love gravity filters.  I hate pumping.

Not crazy about the Katadyn design with the filter inside the bag.

I do like the MSR design.  You can hook up any in-line filter.

They all clog and gravity clogs faster because it's passive.  The force applied by a pump is much more than that applied by gravity.

Air bubbles in the hose need to be flicked to force them through.

The convenience of doing nothing far outweighs the slowness.  Occasionally I filter a whole bag with only 1 L in the bottle, the rest waters the tree.  :D