I have not heard of any “major” algorithm change happening in April. What I can tell you though is that Google’s Eric Schmidt released a statement saying that Google is favouring Brands in their SERPS.

“Brands are the solution, not the problem,” Mr. Schmidt said. “Brands are how you sort out the cesspool.”

Also, there is a possibility that nofollow links are being ignored by Google. There have been tests done on the wikipedia website. A new website was launched with no incoming links to it, they placed a link in Wikipedia with obviously a good article was written about it as well. Within a few days the website was indexed by Google..

My personal opinion is that Google is looking at the major websites with a high reputation and is ignoring their nofollow links. I don’t think every site on the www is able to do this though…