A WebmasterWorld thread notes that if you do a site command search using SITE: versus using site:, Google will return different results.
For example, lets compare site command results for the Search Engine Roundtable.
In the lowecase version, you see:
In the uppercase version, you see:
Notice how Google is finding results for the phrase "SITE:www.seroundtable.com" in our uppercase version. In contrast, in our lowercase version, Google is returning the number of pages they found indexed.
Why is there a difference? I am not sure.
Forum discussion at WebmasterWorld.