The Dictionary: Pros and Cons?

In you guys' opinions, what are the most powerful aspects of the dictionary data structure? What are the biggest drawbacks?

Recently I've been mulling over some different structures which fulfill this purpose. At least a little of this change is motivated by automatically managed memory. Some of the change is motivated by my desire to break away from space-delimited word-bound input, and in doing so squeeze a little more power out of the interpreter. Quite a bit more of this change is motivated by Lua's own table structure, which I'm sure at least some of you will confess is similar in function.

So I'd like you guys' opinions on it. Specifically, what could be done better; what features you'd all like to see implemented no matter how difficult or esoteric; what things does the dictionary make hard to do? Is the FORGET keyword overrated? Is word re-naming a great feature? Are nested dictionaries a good idea? What about one-off functions?