With no visual cues, users probably won't notice a difference between Google "Caffeine" and the current, presumably de-caffeinated version.
Google doesn't normally announce when the company has overhauled its search engine, especially since it tinkers with it all the time.
The result of those long, late hours mainlining coffee? Google "Caffeine," a premlinary release of a newly engineered version of the company's core competency, its search engine.
If you want to try it out, don't be surprised if you can't see much of a difference -- because visually, there is none.
Instead, you'll have to trust Google (and most of us do) that the improvements to speed and accuracy are real and not just a sandbox project made public because the public relations department was scrambling to win some press in the wake of Microsoft's moves.
Google famously doesn't like to advertise, so maybe the company's lack of experience in that department is why they didn't give users something -- anything at all -- as an obvious hint that the new search engine is different.
Besides the cryptic "sandbox" site URL, that is.
Jackson West prefers to just let go and let Google when it comes to search.