
You've seen this guy before. Hes one of the most famous
infomercial hosts in television history (although this guy is gaining fast). His name is Chef Tony, and he sells the Ultimate Chopper.
ZOMGWTFBBQ am I talking about? STFU, k?1! YOU, silly rogue. Ask yourself, how often do you use slice and dice? Yeah, yeah, I know. Even a noob rogue knows this should be one of his or her most oft used abilities. But do you really, I mean really, know how important it is to your overall dps output? Take a look at these, a very simple set of calculations to understand the mechanics of the skill.
First, your overall dps is determined by a combination of your main hand

OK, so, back to that 349.5 number. Simple enough, 201.2 + 148.3. Any idea how much of an increase slice and dice adds? Well, itd be better to think of slice and dice as addition by subtraction. That is, from your attack speed. By 30%. My main hand dagger goes from 1.80 to 1.38, my off hand from 1.50 to 1.15. Here comes the fun stuff.
In order to figure the damage per second of either main or offhand, you first need to take the average between their respective minimum and maximum (which is affected by attack power and stuff, I just dont feel like looking it up).
Main Hand = ([394 + 330]/2)/1.80, or, 201.1, uh, 201.2 (no idea why the tooltip doesn't match).
Off Hand = ([241 + 204]/2)/1.50, or, 148.3.
201.2 + 148.3 = 349.5
At rank 2, Slice and Dice reduces attack speed by 30%.
1.80/(1+0.3) = 1.38.
1.50 /(1+0.3) = 1.15.
Now...
Main Hand = ([394 + 330]/2)/1.38, or, 262.3.
Off Hand = ([241 + 204]/2)/1.15, or, 193.4.
262.3 + 193.9 = 455.7.
455.7 - 349.5 = 106.2
What does this all mean? I am gimping myself one hundred six and two-tenths (106.2) points of damage for every second that I do not have Slice and Dice up.
Over one minute? 6,372.
Remeber 20,970? Try 27,342.
Now, do this using your own numbers, and ask yourself, "Do I pay enough attention to Slice and Dice?".
Note: The above calculations and statements are made with the intention to apply mostly to instances and raids.
Dislcaimer: Due to the author's mathematical ignorance, the above calculations are subject to be completely wrong. Well, this came true, as GSH kindly pointed out. I adjusted my terrible calculations and viola...I fail.