I've been self hosting Vista on my laptop since sometime in January. Every Monday morning, without fail, I installed the latest build available from the "main" windows branch, and tried it.
There have been good builds and bad builds - the first few were pretty painful, everything since sometime in March has been wonderfully smooth.
But sometime late in May, things changed for the worse. Weekly builds installed just fine on my main development machine, but my laptop would get about 3/4ths of the way through the install and stop after a reboot complaining about a problem with the critical system driver <driver>.sys.
Of course, I filed a bug on the problem and moved on - every week I'd update my laptop and it'd fail. While I was away on vacation, the guys looking into the bug finally figured out what was happening.
The first part of the problem was easy - something was causing <driver>.sys to fail to load (we don't know what). But that didn't explain the unbootable system.
Well, the <driver>.sys driver is the modem driver for my laptop. Eventually one of the setup devs figured the root cause. For some totally unknown reason, their inf has the following lines:
If you go to msdn and look up DDInstall.Services, you get this page.
If you follow the documentation a bit you find the documentation for the service install section which describes the StartType key - it's the same as the start type for Windows services.
In particular, you find:
So in this case, the authors of the modem driver decided that their driver was a boot time critical driver - which, as the documentation clearly states is only intended for drivers required to load the operating system.
So I'll leave it up to you to decide - is this an example of cargo cult programming, or did the authors of this modem driver REALLY think that the driver is a critical system driver?
What makes things worse is that this is a 3rd party driver - we believe that their INF is in error, but we can't fix it because it's owned by the 3rd party. Our only choice is to baddriver it and prevent Vista from loading that particular driver. The modem chip in question hasn't been made for many, many years, the vendor for that chip has absolutely no interest in supporting it on Vista, so we can't get it fixed (the laptop is old enough that it's out of OEM support, so there's no joy from that corner either - nobody wants to support this hardware anymore).
Please note: This is NOT an invitation for a "If only the drivers were open source, then you could just fix it" discussion in the comments thread. The vendor for the modem driver owns the rights to their driver, they get to choose whether or not they want to support it, not Microsoft.