Windows XP uses under 100MB memory for my install with the services I don't need disabled and some useless preboot items disabled, windows xp uses about 40-45MB of memory at startup
Keep in mind that the minimum requirement for windows xp is 64MB ram and a 300MHz CPU
If microsoft wants windows 8 to work on a tablet, they need to do better, they need to bring the requirements down to windows 98 levels (ignoring CPU instruction sets and functionality, instead, just in terms of raw performance)
the goal of the OS should be purely to be a platform to to run the programs that you like and stay out of the way as much as possible and use as few resources as possible so that more will be left over to run your programs as quickly and efficiently as possible with the hardware you have.
other than that, it needs good file managementand abilities to customize, and if you feel a need to make it bloated, have a advanced option where before installing, you select what services you want, what gui elements you want and a whole host of other items.
Regardless of what some here might think, not everyone needs every single window service and GUI element and all of the other crap that it comes with. allowing a user to customize what gets installed will help with getting a OS that is as efficient as possible for the specific user of the system.
If you were one of the people who upgraded from windows XP to windows 7
The install size grew from 2.7-3GB to upwards of 20GB
Compared to what you regularly do on your computer, how much of that extra 17GB or so of bloat added into the OS are you using , how much of it do you need.
There are stripped down versions that only take 10GB and you generally cant tell the difference (I have tried one, though I wouldn't use it as I don't trust that nothing malicious was done)
Anyway, not everyone needs everything that comes with windows, and anything extra they don't need is simply a waste of resources.
If microsoft wants a truly good OS, restrict the developers to modern computers that have been downclocked to around 200MHz and only have 256MB ram and have them design a OS that supports the modern hardware but runs fast with the limited CPU speed and memory