Search Server is one of the other major Enterprise servers of Microsoft which is growing Fast with Sharepoint 2007. With the new release of Search Server 2008 in March, it is expected to take Search functionality and Search Experience to the next level for Microsoft's Customer's.
There are better features than Google's Onebox Search Server Appliance, though I would say both have their own pro's and con's.
Search Server 2008
It's RTM version's are getting released in Express and Full Edition. Express Edition will be downloadable for free whereas Full version is a licensed product. There will be support provided for both these versions from Microsoft.
Express Edition's limitation is that it can be installed only on a SingleServer WSS 3.0 environment, whereas, Full Edition can be installed in a Farm WSS 3.0 enviroment.
Search Server 2008 MOSS patch is expected to be released later this year. When you install Search Server 2008, WSS 3.0 will be installed along with it, with some more cool features of Search which is not available with only WSS 3.0 Another new and cool feature of Search Server is the Federated Search which allows you to render the index of the Search engines on the internet, except for Google Search, Google blocks any search engine to crawl its content.
Search Server needs to get the results returned in XML formart to display those results in the Search query, for any Search engine that cannot return the results in XML format to Search Server, we have Federated Search custom connectors that can be created to re-format the results in XML format and store it locally. Those custom connectors is something that Shareopoint Developers will have to do. There are many 3rd party custom search connectors already available and can be used with Search Server 2008.
Google's Enterprise Search products have limitations of crawling data, depending on the product you buy, the limitations differ. In Microsoft Search Server 2008 there is no limitation to the no of files that be crawled. Also, Google's product expire in 2 years and so will their email support, they do not have any on call support. If you want to renew the support you will have to buy a new license for that to get support. (Email)
More information on the Installation and new features of Search Server 2008 will be posted soon.