I'm already hearing all sorts of disaster stories involving Windows Vista, Office 2007, and non-Microsoft applications:
Applications crashing. (LOTS of Explorer crashes being reported).
Companies refusing to release updated drivers for things like 2 year old printers (and other hardware - e.g. video cards).*
Application UI problems - ranging from visual artifacts to complete unusability.
Applications refusing to run.
VPN software not working right or at all.
* Microsoft apparently hosed the Unified Driver model for Vista so one driver package can't be used for multiple devices. ATI and Nvidia are up in arms as is every hardware manufacturer...so the various companies are just making drivers for their latest devices to cut their losses. Hurts the consumer, but there is no way around it unless Microsoft fixes this big blunder. Idiots.
Haven't heard of any data loss or BSOD scenarios yet, but given that a lot of hardware and software doesn't even work under Vista, I'm not surprised. However, given that Vista has been out for roughly two weeks and every IT admin I run into is saying to their users to downgrade back to XP if they want to connect into the office from home, Vista has some major issues to work around.
Then there are software developers who have put Vista on their primary development PC. If you are developing software under Vista, complete with version control and other development tools, you are an idiot. Running Vista under VMWare or VirtualPC to test your software package is fine - or even a dedicated test box, but putting it on your main development PC is just plain stupid. It is going to take multiple service packs (3-5 of them) to stabilize the OS back to XP's level of stability. XP really needs one more service pack (SP3) of stabilization fixes but SP2 is good enough - anything less is pretty unstable. If you bought Vista, take it back to the store and un-buy it. Same goes for Office 2007 - half the plugins out there don't work (e.g. anti-spam plugins)...sure most plugins will eventually be fixed (assuming it is even possible), but if you need the functionality now, you'll be out of luck.
Besides, XP and Office 2003 do just about everything anyone might want to do. The only thing Vista and Office 2007 do is chew more resources to display stuff in 3-D and run significantly fewer applications. At the time of this writing, that is a huge waste of $500+ that is better spent on an application you actually need.