According to a couple sources, it actually sounds as if the first beta of Windows 7 (possibly still codenamed "Vienna," although I haven't heard it called that name for quite some time) will likely be dropping before the end of the year.
Mary Jo Foley, an author on all things Windows who I particularly enjoy reading, has made it known that she belives that Microsoft will not introduce Beta 1 at either PDC (October) or WinHEC (November), two upcoming Microsoft conferences. Although, she does mention that it appears as if Microsoft will be on target for a mid-Decemeber release of Beta 1, which would mean it would be public in beta form for about a year before its consumer release target in early 2010 (NOTE: Many people posting around have now seem to come to the conclusion that Microsoft is dead set on late 2009, but they've said 3 years after general availability of Vista, which was January, 2007, so I still look at it as early '10).
However, there is another source claiming that Beta 1 goodness will reach the public even earlier than December. Andy Patrizio at InternetNews.com apparently has a source that puts the RTM release of Windows 7 in June, 2009, and a Beta 1 release at PDC. In fact, Patrizio believes that the Beta 1 will actually be released to the general public on the first day of PDC, October, 27.
Considering I'm a tech guy, and love beta testing, I really hope that Patrizio is right. For those of you out there thinking a 2009 release means that certain proposed additions to Windows 7 will get cut as a result of the early release, you're really missing the main thing here:
Windows 7 will NOT, mark my words, be a major OS release. Those who have tried, or currently have, Vista will be surprisingly familiar with 7, because it will simply be Vista +. Is this a bad thing? No. I assume Windows 7 will have all the reliability that Vista will have one year from now, which should mean the OS will be pretty stable.
Upgraders from XP who initially tried to upgrade to Vista in 2007 will probably say "wow, this Windows 7 recognizes a lot of my devices, and never crashes on me!" Well, guess what, Vista in 2009/2010 would do the same thing! Windows 7 is going to retain the Vista kernel, and devices that work under Vista will also work under 7. Windows 7 will simply add the touch capabilites, Office ribbon, and faster boot times that have already been talked about.
If you haven't upgraded to Windows Vista, you may as well try it out, because what it represents as an OS will be the Microsoft standard for the next few years to come.