MacRumors.com

Computerworld digs up evidence that the 13" Aluminum MacBook appears to have gotten a quiet screen upgrade as of late April. The blog post references findings by MacRumors forum members fuz10n and hellfire88. Hellfire88 had access to both a Unibody MacBook from November as well as one of the newer ones and posted comparison shots. The two screen model numbers are 9C89 and 9CA5 respectively.

It can be hard to see the differences in the photos, but the user also describes them in day to day use:

I personally see a difference in person when I use them both, but others may not. The newer one seems to have much deeper blacks and better contrast. I'm not sure its as good as the screens in the uMBP's but IMHO its definately a "step-up" from the original uMB screens.

Computerworld reports that the new screens are similar to, if not exactly the same, as the screens found in the MacBook Air. Retail Apple Stores that have been checked seem to still have the original (worse screen) units on display.