This is a bit of a bugbear of mine. In future updates, can the output of double-quotes instead of single-quotes be standardised?
I always like to develop my themes using XHTML 1.0 Strict, so ensuring that the final theme is valid and tag attributes are wrapped with double-quotes is an important factor.
Here's one example. The wp_head hook contains the following line of code:
<meta name='robots' content='noindex,nofollow' />