MISHA I've used this sporadically and it's actually a pretty solid reference tool, especially for $1.99. It doesn't have the breadth of Oxford or AHED, but it's also a fraction of those prices.
One thing that's annoying: the word you entered isn't retained between portions of the app. So if you try to look up a word in the Dictionary that you're not spelling correctly and then switch to Spell Check to find the proper spelling, you have to re-enter your word there.
But overall, a good value for the money.
(Version 1.1)