ulytau,
I bought a fast new computer with Windows Vista a few years ago. Out of the box (that is, with maybe one or two applications like firefox added, and nothing else), it would randomly freeze for 45-90 seconds while doing things like web browsing, and that within 5 minutes of booting. Occasionally it would never unfreeze.
Was this a configuration issue? Maybe. Should it be possible for a preconfigured OS on new hardware to run that badly? No. Did many, many others have similar issues? Yes.
(The computer ran, and runs linux blazingly fast and with no hitches at all. It also runs pretty well now with Windows 7.).
Even the less spectacularly bad OSes, like XP and 7, are slower than they should be, which is to say, it is difficult to configure them to run everyday applications as fast as Linux easily does. They also consume a great deal of RAM, even without applications running, and it is hard to impossible to configure this away.
As for viruses -- sure, you can run antivirus software, which will slow your computer down even (substantially) more and cause various inconveniences besides; or you can run an operating system that never gets viruses even if you don't run antivirus software.
There are various reasons Linux is virus free. One of them is that too few people use linux for viruses to propogate efficiently. Another is fewer security holes and a generally more robust security system. (This gap has narrowed over the years).
"Doesn't act like you want it to" means that it's woefully unconfigurable. Notice how every time a version of Windows comes out, people talk a lot about how great or awful some or other UI feature is? That happens a lot less on linux (other than ubuntu), because there's such a vast array of different ways you can set up your desktop that at the end of the day, it will pretty much look and act however you want it to. Windows sometimes improves in these respects, but then sometimes, it takes a huge step backward. Whatever it does, you're pretty much stuck with it. You're not going to be able (for example) to completely replace the desktop system, as you can in linux.
And even apart from the UI, it's pretty much going to do what it wants to do, how it wants to do it, and you're going to like it or leave it.
I use both Windows and linux regularly. So far as I can tell, your encounters with the latter have probably been limited to reading stereotypes.