Fantastic! Simple and straightforward. And unobtrusive, to boot. The easiest and quickest way to add proxies and rotate among them.
Only one suggestion for improvement: please make the Current Proxy field blank if none of the proxies currently at work. Once one turns a proxy off, the field should become empty, without showing the top one on the list. There's always a risk of accidentally removing a valuable proxy if it happens to be this top one.
Otherwise, just excellent! (Sometimes it seems the proxy lingers for some time after turning it off. Very weird feeling, though.)