Firstly, i think this is a really good app, straight from the start you can create really good icons for apps and logos. This is without too much thought or trouble.
The icons are excellent and would work for most users.
I do think that CandyIcons are still in earlyish developement, by that, I believe they will scale the functionality of the site further.
For instance, maybe they can add something that helps with styling of a particular icon of some further functionality that provides deeper tweaking once you find something that works.
Maybe this isn't possible, perhaps, but I'm sure there are further feature developments on the horizon.

Normally, I'd play with an app like this and lose interest but I can see already that this is very useful and will be beneficial in adding icons to the armoury and is therefore a keeper...

Not too bad at all... and worth investing in for sure...