The issue Kelly above describes is not exactly the same as what I experienced -- I was using IE, not Firefox, and I had instant search on. However, it's quite a relief that this turns out to be a bug after all.
This is a glitch. It happened to me yesterday right after I read this thread. Just one page. No images results at top, no search box at bottom.Just to see what might happen I clicked on the "instant is on" button (turning it off) and the page reloaded with images and search box. I found that if I clicked on page 2 it returned to a single 10 results page, but if I clicked on page 3 or further, the search box and series of page numbers for results remained intact. I tried this over for about 5 times and got same resuts. Once you skip past page 2 everything is normal. It's definitely no "test" (at least not a test to see how everyone likes only one search results page. That would indeed be ridiculous. It's broken. Looks fixed today so far.
Google constantly delivers different things to different users who have input the same search. Their infrastructure is extremely complex, using hundreds of thousands of computers. Load balancing alone must involve a mountain of code.
I'm just having a bit of fun, so don't take it to heart. It's a good thing to think critically about whatever Google says. Just don't fall into the trap of automatically assuming the worst every time - or drinking all their kool-aid, either.
When it comes to tests that are seen and reported in forums, they've been really straight. They sometimes just say nothing at all - but as official comments go, this one just seems straight to me. I've been a Google watcher since the "backrub" days.
Actually I think they'd rather call this a bug - even if it was some test. Which is not unlikely. Together with "Instant" it could very well be that somebody at Google had the idea to only display a fraction of the results and force the user to refine the search query, getting new results while he is typing.
But since the recent emberassing display of background images they had to kill of the day the came out because user where complaining they would probably rather admit a bug than another "feature" gone wrong.
The problem with being a thousand pound gorilla is you must stay on the path or you'll crush something only a foot away. I try stuff all the time and if it doesn't stick it affects only me, so I change it. Whether this was a bug or a test, the result is the same ~ all of us little creatures start yelling "watch out, you're hurting us". Anything they try will potentially make a mess of things for some parts of the user base. This was a particularly bad stray from the path, so I'm relieved to see they won't be pursuing this line of thinking, and gladly accept any reason for bringing it to a halt...