mattur - 11:39 pm on Feb 25, 2012 (gmt 0)
No need to use aria-labelledby here. The <label for=> relation labels the input effectively for everyone so adding aria-labelledby would just be accessibility theatre.
See this blog by a Mozilla accessibility QA engineer for an example of where aria-labelledby could be used [marcozehe.de...]
As a rough rule of thumb do not use ARIA at all unless you 1. need to because normal HTML semantics do not cover the usage scenario 2. are an expert and 3. are going to test in AT.
Despite WAI-ARIA 1.0 currently being a W3C candidate Recommendation, even the W3C Working Groups involved can't agree on how some parts of it work/should work. Expect a rapid release of WAI-ARIA 1.1 :)