If you actually have the graphics and design skills/resources, and the ambition, by all means do it yourself. Thats the only way you can, as my friends in the corporate would would say, 'realize your vision'. Or better, make your own re-usable GUI framework that you can use in other applications. Dont be dissuaded by mantras about re-use if you really want to do it yourself.
On the other hand, if you dont have those resources, either use a 3rd party toolkit, or re-consider the need for an 'outside of the box' interface. You'd be doing your users a favor. The only thing worse than a bad interface is a bad, ugly, home-grown interface.
I dont know what kind of apps you are making. But if we are talking normal windows/desktop apps, evaluate whether or not your 'outside of the box' interface is something thats actually good for the user. I've seen many apps with atrocious interfaces over the years because their developers didnt want or couldnt care to create an application that more or less followed interface norms. That creates a lot of unnecessary overhead on the user as they try to learn your product. And the thing is, their developers dont realize their interfaces are that bad. So unless you are working on the type of app that calls for something 'slick' (like a media player or game), if you dont have the resources do your users a favor and use a 3rd party or standard (for the particular platform) interface.