First off I've never used Vista. (Although I am generally a Microsoft fan). I also supect I'll be avoiding Vista for quite some time to come. (Not that I have the money for upgrading to be an option right now anyways).
I'm sure there is hatemail about all versions of Windows, but I think the recent arguments against XP and Vista are inherently different than previous arguments, and certainly very valid. Generally when you upgrade, you are offered more features, and may have to put up with new bugs. But with XP and Vista, Microsoft has been adding stuff that can be purposefully bad for the end user.
I'm rather fond of XP as it certainly does add a few nice features, but what happens when they no longer support it? Will you still be able to activate it after you install? Or will it just be a crippled OS that doesn't run for more than 30 days before requring a new install. (Or you'd need to do something that's most likely illegal). Same deal with Vista. Basically you no longer really own the OS that you "bought".
Activation is mainly there to prevent pirating (which happens anyways), but I kinda wonder if they'll ever use it to force you to upgrade to the latest greatest copy of Windows by refusing to activate old copies of Windows. Mostly though it's just a pain to legitimate users of the end software. Especially if you plan to upgrade hardware, or want an installation that isn't connected to the internet.
The thing that many people are against Vista for is DRM (Digital Rights Management). Definately a lot of hatemail on that one. Although, some of it seems a little uninformed. The DRM scheme is supposed to only allow high definition (above DVD quality) playback on supported devices. If the device doesn't support it, then it purposefully degrades quality (down to DVD quality) or prevents playback entirely (but this sounds like the less likely option, and is apparently set by the content publisher). I've also heard that Vista performs self checks to see if you're trying to defeat the DRM system, and spends CPU cycles doing so. You can probably guess why many people find this offensive.
Now that isn't all Microsoft's fault. The content providers want this protection built in. If Microsoft is going to support the new media, they supposedly need to support the whole DRM scheme. What many people are really objecting to is the DRM scheme. Although, there is speculation that the self checks actually take a significant amount of time, and there is the issue of of whether or you have to pay the price of those self checks whether or not you're using the feature. I've read one article that suggested you did, but it seemed a little overly hateful, so I'm not too sure. I've also heard various concerns about hardware needing to meet certain standards. The whole DRM scheme isn't too useful if some expansion card can pick the data off a system bus, or a device reads it from the video card output. I've heard stuff suggesting many hardware devices would need to meet new requirements, mainly to ensure system security, but this doesn't seem to be the case implied by most sources. What is required however, is that the monitor must support decrypting the video channel to get the protected content to play. This means you'd need a new monitor to support playback at full high definition resolution. If your monitor can't accept and decrypt the video channel, then it gets degraded before being sent so it can't just be picked up off the system bus or video cable in the original high definition. This sort of leads me to wonder if people will try hacking their monitors though.
Buying a new monitor that supports that is expensive. I've also heard further concerns that a lot of old monitors (and other hardward devices) will be thrown out as people upgrade to comply with Vista's requirements. Sounds like this rush to upgrade may have been a little overhyped due to all the misinformation, but still, there was the issue of what happens with all that computer waste that will be generated. Electronics usually contain toxic elements. The solder used to bind the components to the boards often contains lead. But, you shouldn't have too worry about that too much since a lot of that waste gets shipped off to poor third world countries where it won't hurt you. So very moral. (Maybe people should pay more attention to computer and electronics recycling).
I've also heard a little note about how Vista handles games that people here might want to take note of. Apparently there are parental controls that can be used to disallow kids from playing games with bad ratings on them. If the game isn't rated, it's basically counted as adult only. A lot of parents will probably have settings to disallow such games being played. Sounds good, but only if getting the game rated isn't a problem. Seems getting those ratings can be a rather expensive process however. Pretty much only the big studios with money will really be able to pay for this. The built at home variety just won't run if the parental controls are used. Big businesses will probably approve, as they'll have less competition to worry about from small startups.
I've also heard there's currently a lot of issues with driver support. Many companies haven't yet got working/bug free drivers for their devices out. It's also supposedly more expensive and time consuming for some to companies (graphics related) to produce those drivers.
So yes, in short, there are a number of things in Vista that concern me. Some of which I feel are counter to how good software should operate. If I'm going to upgrade, I certainly won't do it anytime soon. I'd rather wait and give them time to work out the issues, or maybe I just won't upgrade at all.