I purchased an Echoing Fury the other day with +.23 Attacks per second. I had read that the addition applies to both weapons when dual wielding and it does, but it appears to actually be a % and not a flat +x speed.
My OH is a sword so it has 1.4 aps. If it were added, it would be 1.4+.23=1.63*1.15(for DW)=1.8745.
However, my character sheet says 1.91. If the .23 is a % it would be .23/1.2(original mace speed)= .191666666. This number fits for my OH. 1.4*1.1916=1.66824*1.15=1.918 (I assume the character sheet does not round up) So, the .23 is like have 19% attack speed on your gear.
I am somewhat confused about the MH's APS.. My character sheet says 1.68. 1.43 is the attack speed of my MH but 1.43*1.15=1.6445.. So, I am not sure where the extra .04APS come from.
Also, (1.4+0.23+0.03)*1.15 = 1.909 or 1.91 when rounded up.
3% = 3/100 = 0.03
That only holds if you have exactly 1 attack per second base. If you have a weapon speed of 1.5 attacks per second, 3/100*1.5 = 0.045 attacks per second gained which is actually more than 0.03. Unfortunately, the enchantress just gives you the 0.03 to attacks per second so the dps gain isn't as much as you would expect at faster weapon speeds.