It was announced at Tech Ed that the next major SQL Server version (codenamed Kilimanjaro) will be called SQL Server 2008 R2. This surprised me. I would have bet that it was going to be called SQL Server 2010.
http://www.sqlmag.com/Article/ArticleID/102089/102089.html
Microsoft marketing has to walk a fine line. On one hand, they want to placate any people who are nervous about upgrading to the first version of a major release. On the other hand, they want the products version name to announce that this is the latest and greatest.
Another danger is that in the future, I can imagine ridiculous names for particular versions: Imagine a CTP for SQL Server 2008 R2 SP3.
As for me, when SQL Server 2008 R2 comes out, I’m not going upgrade. I’m holding out for the version after that: SQL Server 2008 Threepio.