Future - Your post and your title here differ in their syntax, but I'm assuming that you're asking about the Google site operator, followed by a colon, and what happens if you capitalize the S in "site", as in....
keyword site:example.com keyword Site:example.com
The site: operator is case sensitive, and when the S is capitalized, Google treats the query not as a site: operator query, but rather as a search that includes the word "site" as one of the search terms.
I've never found official Google documentation to confirm that the site operator is case sensitive, incidentally.
I should also add that, on my machine anyway, if I do one of the above searches right after the other, the new Google ajax interface isn't always responding to a case change immediately and I sometimes need to refresh the page after doing a search.
in the very small sample i ran [Site:example.com] results were similar to [Site example.com] with a small increase in reported results for the latter. what really surprises me is the difference in reported results between [Site example.com] and [site example.com] in a few of the cases i tested. i may try some more testing here later to see if i can discern any pattern or explanation.
in the very small sample i ran [Site:example.com] results were similar to [Site example.com] with a small increase in reported results for the latter.
Theoretically possible, of course, but in the tests I ran, results are generally more like what Lame_Wolf reports. You want to try this with a domain that's likely to be mentioned on the web beyond its own pages. If you try a few domains of different sizes, chances are you'll be seeing the differences.
Also, to assure yourself that there's nothing mystical about [site example.com], try searching [example.com site]. Number of pages returned should be close, but because Google estimates this number, it won't always be exactly the same.