Two questions regarding putting:

Question 1:
Per rule 16-2 regarding an overhanging ball - why must you add a penalty stroke?
"16-2. Ball Overhanging Hole
When any part of the ball overhangs the lip of the hole, the player is allowed enough time to reach the hole without unreasonable delay and an additional ten seconds to determine whether the ball is at rest. If by then the ball has not fallen into the hole, it is deemed to be at rest. If the ball subsequently falls into the hole, the player is deemed to have holed out with his last stroke, and he must add a penalty stroke to his score for the hole; otherwise, there is no penalty under this Rule."

Question 2:
If you are on the putting green and you mark your ball after it comes at rest. However, when you attempt your putt, because of conditions and location, your ball keeps moving, making it impossible to putt from your marked position, what do you do? (ball on a slope of a fast green, with strong winds).

Answer 1 : Don't know - that's just the way it is. Maybe it's because it has been holed without actually touching the ball - see next answer.

Answer 2. Once the ball is replaced, it is in play. If the wind (not an outside agency) subsequently moves the ball, it should be played from it's new position. This applies wether or not the marker has been removed. See rule 20-4 and decision 18-1/12 and 20-4/1. Since the balls new position in answer 1 is in the hole, it cannot be played from it's new position and hence a penalty stroke is added. Seems fair to me as you are not required to putt.

so for question #1, you need to mark that puppy ASAP after you wait 10 seconds (to see if the ball falls in) or face a 1 stroke penalty?

Yep. I remember Sam Torrance running to his ball in one tournament after copping a ten second penalty the week before.

Wouldn't the penalty stroke just be the tap-in stroke that you SHOULD have taken, had you not waited more than 10 seconds?

yes... you are exactly correct

One thing you "do" is hope that you have not addressed the ball after you put it back down, because if it then moves you have a penalty stroke and must replace the ball.

Another thing you "do" if "your ball keeps moving, making it impossible to putt . . ." is you suspend your round because the conditions are unacceptable. That's what the PGA Tour does.

What it means is, tap it in after NINE seconds.

No need to mark a ball that is overhanging the hole.

I have a funny story about #2

I was watching an LPGA event earlier in the season, it was SOOO WINDY out, this girl marks her ball picks it up and waits her turn...

When its her turn to putt she places her ball on her mark, lines it up and backs away....a HUGE gust blows across the green takes her ball, rolls it off the green down the rough into the WATER HAZARD! costing her a stroke...man that would SUCK!