Note: Please read this post in its entirety before asking questions about the sheet. Your question is very likely answered here. If you ask stuff that I've already answered, you *will* get infractions, and they *will* be vicious.
Q: Why do all my socketing recommendations sometimes change when I make minor adjustments to my gear?
A: Whenever you change what stats are on your gear and socketing, the value of all other stats changes slightly - this is why we have spreadsheets, rather than a static list of EP weights. The important thing to keep in mind is that the sheet isn't really recommending full sets of optimized gear; it's merely making a list of items that are probably good, and to do so it assesses them as though they're socketed with whatever your current top stat is. However, if your top stat changes, so does it's socketing strategy. So, for instance: as you socket more AP, the value of other stats (such as Haste) increases; hence, when you reach the point where Haste's EP value passes 2, it will suddenly start recommending haste gems instead of AP gems. All this means is that your top stat changed. In order to optimize in this situation, you simply need to play around with your available options and see which one yields the highest DPS estimate.
Q: Okay, I understand that, but I'm getting some really huge spikes in stat value, particularly with hit, expertise, crit, and agility. Why are my EP values jumping all over the place?
A: Many stats have soft or hard caps now. In particular, if the "base crit" and "crit cap" cells turn red, that means you are crit capping when one or more procs is active; this will result in skewed EP values for Agi, Crit, Hit, and Expertise. Hence, as you move back and forth through various crit caps, your stats will be jumping all over the place.
Q: Why isn't it telling me to socket expertise even though it has a high EP value?
A: Because by default, expertise socketing is disabled. Check the settings tab if you want to turn it on.
Q: Okay, I did that, and now it's telling me to keep socketing Expertise way past the cap.
A: Yep. It isn't doing slot-by-slot optimization. It's stuffing everything with the best stat, even when it doesn't make sense. That's why Expertise gemming is disabled by default.
Q: Item X is missing from the sheet, why isn't it included?
A: Because it sucks.
Q: So, I opened up some of the hidden sheet to edit gear/add gear/play with the modeling, and...
A: You broke something. Not my problem.
Q: Does the sheet account for...
A: Okay, I'm sure there are things I haven't actually accounted for - the sheet is by no means perfect. However, unless you have specific reason to believe that it isn't modeled, it probably is. If it's something basic, the answer is definitely yes, unless I've specifically mentioned it previously in this post.