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 :First of all, memory usage of many OSes is, to put it mildly, absurd. 
 :XP was quite bad in that regard when it came out, mostly because it was the first ""NT"" OS for desktop PCs. Before XP, one used to have 98, which came with its own DOS, and took about 16 megabytes of RAM and 120 on the HDD to run almost decently. XP, however, took 128 megabytes of RAM and more than 1G on the HDD. Not the minimum figures but the ones for decent performance. I was a late adopter to XP as well (late 2005/early 2006). By then, PCs were quite XP-capable. 
 :Vista was quite disgusting. It was like MS doubted themselves that they could make anything better than XP. They started with a name of ""Longhorn."" On top of that, Vista came with a RAM footprint of 512M (and that was more sluggish than XP at 128) and an out-of-this-world 15G on the HDD. 
 :That's a factor of 6 (I'd guess it would run as fast as XP on 128 then) to 10 compared to XP. And all that for the sole purpose of implementing... 
 :Wait... no, that's not quite it. Hold on another sec. 
 :I give up. Beats me what the heck they implemented. ( 
 :To make a long story short, one has a new Windows, and that's it. Its GUI is queer, it's incompatible to XP either, and its footprint is absurd. There might be some changes under the hood, but it all boils down to the car analogy, ""Yeah, the engine block is a bit on the heavy side, 5,000 pounds is the heaviest so far, by far, but we achieved a 5% better fuel economy. If your vehicle weighs in at 100,000 pounds or more, you'll be glad you bought our Vista engine."" - Which means that the car will consume more fuel not less. Unless your other car is an Abrams. 
 :BTW, I doubt they achieved as much as a 5% savings. 
 :I read one post once where somebody wrote that MS ""made his computer look like one of those digital atrocities in CSI Miami"" , and from the quick glance I had at Vista, he's right. There was talk about the memory growth which is still exponential (although post-Vista OSes are not that bad at it - they still manage to shave some megabytes off without major sacrifice) while the feature set was approaching a limit. I'd say it's not that bad, but it could be logarithmic. ;) 
 :Personally, I don't care a bug's ass about all the ""features"" they keep bullhorning - I don't want a tablet, I don't need one, and I would prefer a sleek little OS that runs my programs the way they're meant to run. I don't need a 28"" HD display either. I don't write my letters in landscape format, and even if I did, a 4:3 display would have the width for it. I don't want a 3"" display in portrait format either - and I don't want any hardware by companies struggling to assemble a decent phone. But I digress. 
 :DOS was made in months if not weeks, by an 8-man team to boot, and now MS can't come up with a decent successor to XP? In one decade??? My thought is they could but why try if everyone's gonna buy Vista, 7 etc. anyway. If the vast majority of customers were reasonable enough to abstain and continued to use XP, they'd be amazed at how quickly MS would come up with something better. They did it once, when Vista didn't sell too well. One could only guess what they would have come up with if Vista had sold even worse. 
 :About the ""We won't support XP beyond 20xx"" threat, I can only say ""LOLwut? Is u serious? We cease to buy your craptacular OSes and your threat is to cease to break XP?"" As blatant as some security flaws are, other companies are quite up to the task of fixing them if MS don't. And they would not mess up the processes we do want on our PCs. Actually, some security suites made quite a mess (deleting SvcHost.exe is my all-time fave) but at least not as regularly as, say, SP2 did. 
 :Bottom line, XP was steep when it came up, but its successors are completely off, and they don't begin to come up with anything significant. Changes - lots. Advantages - no. There's still no decent multitasking support. For example, menus close when a different window steals focus. And there's not evena DOS-style ""Abort/retry/skip"" choice when one of a batch of files cannot be copied or deleted. 
 :I won't say anything too subjective about Bill G here - WP:BLP and stuff - but if there's consensus that ""living"" is to be judged by brain activity, Bill could be in for a good whacking... - ¡Ouch! ( / ) "