Ed Bott has done some really good work getting to the bottom of Windows Vista startup times on a number of different systems. The conclusions are pretty much as I expected - bootup times depend on the system being tested. I've now got a question of my own - why are people so bothered by startup times anyway?
Think about it. How many times a day do you boot up your PC? If you do this activity more than two or three times a day on a regular basis then you're not making proper use of the features that your PC offers, such as hibernate or sleep. Trying to measure stability is as useless a metric as boot time. My systems can go for days, and sometimes weeks, without a reboot, being hibernated/put to sleep at the end of the day or during any big breaks in the work day. In fact, I like the hibernate feature a lot because it lets me shut my systems down yet leave my work open. Next time I restart the system, all my apps and documents are open and waiting for me.
Even if I did need to reboot my system a few times a day, I don't think that I'd be all that worried about boot times unless they were really long (+3 minutes) or my system was really unstable and needed rebooting several times a day. In either case, there's a problem somewhere that needs to be solved. If the system only takes a few seconds or a couple of minutes to boot up then I'm really not worried about the effect that the lost time will have on my productivity.
To me, boot time metrics are nothing more than useless information (sorry Ed!). It's a snapshot of how the system behaves at a particular point in time and isn't fixed in any way unless you do nothing with the system (and even then, performance can still be adversely affected by updates that come in automatically). Once you have a load of applications installed, deciding to do all sorts of things at startup (from scanning files for malware to checking with the mother ship for updates) then all metrics go out of the window and all bets are off. I've seen stable systems with boot times that were under a minute slow to a snail's pace over the course of a single reboot. The cause is usually some update that's come in and been applied and it can be really tricky (as well as frustrating) to solve the problem and return the system to its previous performance. This decay over time is the main reason why I'm a big fan of making an image of your system after you've set if up so you can roll back your system to this clean state whenever it starts to feel unenthusiastic.
Sudden changes in boot times are usually quite noticeable, but what usually happens in that boot times grow slowly over time. You start off with a PC with a fresh install of Windows on it and it feels nice and fast (hopefully - if it doesn't then you're in serious trouble and things are only going to get worse, no matter how much you trash your system trying to speed it up). You then install security software and performance takes a hit. Install some big apps like Office and boot times take another nose-dive. I've seen boot times increase by over 100% over the course of setting up a new PC. It's actually quite depressing to watch. But as long as you don't need to reboot all that often and your PC is reasonably stable and you're able to use hibernate or sleep, then it's not really a major problem.
A trap that a lot of people fall into is thinking that an upgrade to a newer version of a piece of software will speed things up. The marketing hyperbole might mention "improved performance" or make some similar claim, but back in the real world where you and I live, I rarely see this work out. If you've PC has problems running XP, going up to Vista is unlikely to be the answer. If your system is sluggish running, say, Photoshop CS2, CS3 isn't going to be the magic speed bullet you've been waiting for. If the company couldn't write tight code last time, what makes you think they can do it now? Similarly, registry cleaners and memory booster software isn't going to bring that smile back to your face. If your PC is struggling, ignore the hype and snake oil and save the money you were going to spend on software and put it towards new hardware.
As Ed quite rightly points out, slow boot up isn't an issue confined to Windows Vista. It's an issue that can affect almost any operating system. Anyone who thinks that these issues are new to Vista hasn't been around PCs for that long.
Trying to measure stability is also just as useless a metric as boot time. Just as I've seen two functionally identical PCs have wildly different boot times, I've seen identical PCs have wildly different levels of stability. This is why I'm always skeptical about PC reviews. You have to put the review (along with any associated benchmark) in the context of other similar reviews, discard reviews that follow different methodologies (even slight differences can have a huge impact on results), and then take everything you read with a pinch of salt and expect your real-world experiences to be different from what the reviews led you to expect.
Thoughts? What metrics are important to you? Is is boot time or something else?