In many cases, when you use your up and down arrows on web pages, the web page will scroll up and down a line at a time. Last week, when Google introduced the blue arrows as a way to navigate the search results with your keyboard, it removed the line by line scrolling.
Now, when you use the up and down arrows on your keyboard, the page may jump down after you down arrow enough to hit the results under the fold. So you don't get a constant scroll using the up and down arrows, the only time the page moves down or up is when the result the arrow is on is not in view of the web browser window.
For some in a Google Web Search Help thread, it is annoying and they don't like it. There are other threads with complaints as well. Personally, I think these users will eventually just get use to it and go on their merry ways.
Forum discussion at Google Web Search Help.