I got the very first samsung model in 2011 which was one of the first two to models to come out after the prototypes. Haven't had a single problem with it, and I love it. Using it right now, and half the time my GF uses it instead of her macbook pro because it is easier to just pick up and use(faster boot, lighter). It also gets abused a lot more. Low price and no fear of losing data we are sadly more careless with it than a tablet. Picking it up one handed, leaving it on the edge of surfaces... dropping it... there is currently a coffee stain on its white shell... Regardless it works as well, no BETTER, than the day I bought it(thanks to more apps and updates).
Yes multiple users can be on it. Your 'user' is just your gmail account. So actually you can log into ANY chromebook using your gmail account and everything should carry over. You won't be able to access anything else someone has saved on the hard drive of the other chromebook or anything you have saved only to the hard drive(so not cloud) of your own chromebook, but otherwise it will work just like the one you have.
Say I use Chrome but I'm not signed in, have a dynamic IP address, took other preventative measures (cleared cookies, etc), and don't go to Google websites. How does Google track me in that case?
To do this on a chromebook would require being in guest at all times. Your login is your gmail account. Can't remember how I found it, but there is an option where you can see a lot of the data google has on you... and delete it if you wish. I don't think its everything though, but a pretty good junk. Of course if you try it immediately warns you that it will negatively affect searches and spam filter. I rather like my spam filter, there are 3 new emails in my inbox and 430 emails in spam. No need for a second bogus email address when the spam filter is that good.