usability - Which is more usable: labels above form elements, or to the right?

I'd very much like to get some feedback on this, as of right now, it is a point of contention among the devs at my office and myself. Which is more usable: labels above form elements, or to the left?

Answer

A hotly debated and often rehashed topic. These links can serve to get you started:

http://www.lukew.com/ff/entry.asp?504

http://www.uxmatters.com/mt/archives/2006/07/label-placement-in-forms.php

Top Aligned
Top-aligned labels tend to reduce completion times (how long it takes to complete a form) the most for familiar data (i.e. address, credit card, etc.) because they only require a single eye fixation to take in both input label & field.

Right Aligned
Right-aligned are a bit slower to complete but require less vertical screen space. They do, however, have flexibility issues when the labels change widths.

Left Aligned

Left-aligned forms are the slowest of the three to complete because of the number of eye fixations they require to parse.