Aside from entertainment reasons, what things (physical, mental, social etc) do you learn from gaming?
Depends on the kind.
Games in general (though some more than others) demand a kind of logical thinking to be played well that I believe is very valuable, so I take it as a way to keep my mind sharp. The field of
game theory is a good tool for seeing how the kind of strategic choices we might make while playing a game are really the same as the ones we make with gravely serious matters.
I perhaps take it one step further in that I can never resist modifying games, adding and playing variants to them. I am also constantly inventing new games in my head. It's a fascinating process of constructing and deconstructing concepts.
Physically, games only really contribute if I'm playing athletic sports. I rarely ever plays those, but I'd really like to. I don't exactly need it, though, because I workout and I'm in good shape as it is.
Games do result in the majority of my social interaction. Not only does it create and excuse to come together, but it makes and easy topic of conversation and things lead from there. Usually there is much laughter when I play games with people, and in those gatherings there are almost always breaks where I talk to people about current events, or some philosophical idea I came up with, or some strange zoological fact, etc..
Also, what kind of games do you enjoy playing the most and WHY?
That's tough. Given the chance I will play just about any kind. Video games, board games, sports.
In terms of actual opportunity, I used to play video games the most by far, but now they are about tied with board games. Again, I rarely play sports, though I'd like to.
I'm not sure that I enjoy any form more than the other, but I do enjoy different genres within that.
The video games I enjoy most are probably fighters, or vs games. The ones where you have maybe two to four complex, unique characters fight each for a few rounds or so. Most people know Mortal Kombat, though it really kind of sucks. Others are like Street Fighter, Soul Caliber, etc... Samurai Showdown might be my favorite of that genre. Super Smash Brothers is a very modified member of the genre.
I like them because they involve me more than other games, and I feel like they involve more direct application of skill than a lot of other genres (First Person Shooters gives them a run, though). There's a lot of fun in only competing against one or maybe a few human opponents and nothing else (I am a competitive person). I also feel like there's more depth in ratio to breadth in fighters than other genres. A few details go a long way. RPGs often strike me as having a lot of breadth but no depth, nothing beneath the surface, you see it the first time, you've seen all you ever need to see.
Pokemon is a big exception with RPGs, though.

Those games are ingenious. A lot of breadth and depth. For someone that likes testing, configuring, and exploring things a lot like myself, Pokemon is great fun.
I really like sandboxish games, though they tend to be terribly imperfect. Those are games with a lot of creative control for the player and possibly lacking in a forced goal or actual competition. Black & White and Spore come to mind. They just appeal to my desire to build and create.
God, I haven't even gotten to the other kinds of games yet! It's really hard for me to answer this. I really like games

.
How many hours per week do you estimate you spend playing?
If that includes all forms of games, I'd guess I play about 6 hours a week. Before I was employed or working on college, there had been a time where that was probably closer to 30-35 hours a week.
PS - when answering please keep in mind that I'm not a gamer.
Thank you.
Some of the things I said probably didn't make any sense, if not most of it...