When a search term is too common, you get a message telling you that the search could not be completed. Searching a large database of posts takes time and costs a lot of server resources, so the limits are in place to prevent the servers from being crushed under heavy load. Sometimes a search query takes too long to process, resulting in a database timeout, which in turn causes an error in the search code, leading to a blank page. Easy Search and Google Site Search are nice and all, but they don't have neat integration with the forum software and come with their own branding. Hosting your own search feature for your own site data is much better than trusting a large company to do it for you. I'm sure there are other ways to improve the search without resorting to external parties.