Here's an annoying little bug in Vista. Try it yourself:
From Microsoft Office (in my case, Excel) save two files in 97-2003 format (XLS) and another two files in the standard format (XLSX). Exit Microsoft Office.
Use the Windows Explorer, and find the folder where you saved your files. In the default behavior, Windows will show you the filenames but not the extensions. In "Details" view, there's just enough space to tell you these four files are of type "Microsoft Office Excel."
Here's the good bit: select all four of your files, and press Enter. Oh wait, did nothing happen? Try it again, but this time right-click and select "Open". Nothing happened again, right?
This was very frustrating to me when I stumbled upon this broken behavior in Windows Vista. It took a few minutes before I realized the solution: select the two files that you saved in 97-2003 format, but no other files, and press Enter (or select "Open".) As you expect, Microsoft Office launches and opens the two files. Repeat for the other two files.
The behavior seems to be: if the files all have the same extension, then Windows will launch the "matching" application. If you select a file with a different extension, even if they are all Microsoft Office files, then nothing happens.
If you think this scenario is contrived, then you don't use Windows at work. For example, I'm a senior manager in our office, so one thing I need to do is track time across the different groups. We currently track work time using an Excel spreadsheet. At the end of the week, each manager or team lead under me sends me their "roll-up" spreadsheet, and I create a master "roll-up" for the entire group.
It's easiest for me to go into the network directory where everyone drops off their files, and open them all at once into Excel. This all worked fine when everyone used the 97-2003 file format (XLS). Then one day someone used the new Office format (XLSX), and I was no longer able to open any of the files.
I never encountered this problem when I ran Linux at work. Even if I selected a bunch of different files (for example: PDF, DOC, XLS, TXT ... which can happen when you need to write a document and need to copy/paste from other work) Linux would always act as I expected: it would open all of the documents, using the most appropriate applications. I just tried this test on my wife's Linux laptop, and confirms that it works "correctly".
I know that Vista is full of bugs, but this level of work-stopping bad behavior is going too far.