My take is you won't get the discussion we have of the laws of magic and other stuff like that we have in Your Story, but that Our World makes for a very good general fan guide for the first ten books of the series by itself.
iago probably said it best with the above, but I'll toss my own two cents into the mix.
If you are looking at Our World as a guide to the characters of the series, setting notes and information on the spin on Chicago of the Dresdenverse, then you are spot on. There are some rules-specific things in this book, such as the character sheets of various characters that Harry has run into, but you can ignore that.
You also get some basic information on the Vampire Courts, The Accords, other supernatural entities/organizations, and even a bit of history. It doesn't go too horribly in depth (which can be good or bad, depending on who you ask), but my friends and I are finding it as a great resource when we can't put our finger on the differences between various groups, or when we want to know about a certain character. "Our World" really is a nice looking one-stop shop for Dresden references. Full color, plenty of artwork, and notes on various characters and monsters; what more could you want?
Besides, with the book, you'll have a new short story entitled "AAAA Wizardry," in addition to random flavour text/commentary by Billy, Bob and Harry. And let's not get into the other dashes of humor that is only seen in the Dresdenverse.
If you only want "Our World" as a reference to the series, it is a good one. You will be missing out on some notes (i.e. iago's reference to the Laws of Magic is one of them; there are also references to the various approaches to/thoughts on magic and hexing, notes on human choice versus "monster" nature, etc), but I don't see it as mandatory to purchase "Your Story" if you only plan on using it as a Dresden reference guide.
Long story short: if you want a "Dresden Encyclopedia" (as my friends have so endearingly called it), snag a copy of "Our World." As long as you skip over the character sheets and the references to rules/powers, you'll be fine.
Again, just my two cents. Feel free to take the advice if you choose.
--Crion