I am probably late on this one, but here are my 2 cents. I think we had a 10+ page discussion on this back when I first joined the forum (covered jibs and vang etc as well). Thanks again everyone! Based on the long conversation, and a little collaboration with another sailor here in Jax, I changed over to an upward facing swivel cleat (not sure that it matters, but in case it does my boat uses mid-boom sheeting).
1. With the cleat facing downward, adjustments to the mainsheet "auto cleat". You cannot ease the sheet back out quickly if you over compensate. This was annoying to me.
2. With the cleat facing downward, and you get hit with a puff, it is a real PITA to get the dang thing un-cleated quickly (I would literally kick the sheet to pop it lose at times).
3. With the cleat facing downward, and you get hit with a puff while hiking, it was not uncommon to have to come down into the boat to release it, shifting weight in = more healing in a puff = scary (at least to me). Basically, an unnecessary shift of weight with negative impacts.
4. With the cleat in a 360 degree swivel, tacks and gybes are easier, as the sheet follows you as you re-position.
5. With the cleat in the up position, especially when hiking, it is easy to release and de-power.
6. With the cleat in the up position, you can hold the sheet in hand un-cleated. You cannot do that with a downward facing cleat
7. With the cleat in the up position, you have to pull down to cleat. This requires more effort. Obviously this is preference from one person to another, but I prefer the path of least resistance to lean toward releasing the sheet. Up and and out = easy to de-power.
All in all, I am very happy with the new setup, it is probably my favorite mods. I feel like I have a lot more control, and am able to quickly respond to changes that need to happen. This makes me a less panicked skipper, and I am relaxing more when I am on the water, lol
In short, I vote +1 for upward facing cleat.
DISCLAMER: I did have what I think is the original 40 year old fiddle/cleat combo thing, so more modern cleats probably would have made things I found annoying less pronounced (but I doubt they would have gone away).