IMHO using radio buttons in this case goes against good interface design. Most users "know" that radio buttons are mutually exclusive as a set - only one of the whole set can be "on". Checkboxes, on the other hand, are designed for selecting "zero to many". Go with the flow. Don't turn this standard paradigm on it's head just because you can.
BTW, I just read the following in an ASP book:
When the browser submits the page, it only includes the values of radio buttons and check box controls which are actually set.
And of course, in true fashion of "look at this .. here's something else .. here's a tidbit... " books posing as tutorials and or references, nothing is said of SELECT controls.