1. What OS are you using? (Dual-boot? with what?)
Windows XP and Ubuntu 8.10
2. Why do you use that(these) OS(s)?
Ubuntu, because I love the ease-of-use of it. Some people scold me for not going hardcore and building my own kernel from scratch. To that I say, "to each, his own"...
Windows, because there are two purposes that Linux has not truly mastered yet: Gaming (think TF2, BF2, COD) and video editing (Sony Vegas, Adobe Final Cut). And I just found out that Steam will be making native Linux games soon, including some back-catalogs (TF2 FTW!!!)
3. What advantages/disadvantages does it have?
Advantages? Easy to install, use, upgrade, yadda yadda. Very newbie-friendly.
Disadvantages? I'm not sure, but I know some are there.
4. Related websites?
http://www.ubuntu.com/
http://www.ubuntuforums.org/
5. What should an OS consist of?
According to HP, bloatware.
No, really, it should have solid support, a good developer backing (programs, security, etc), and most important of all, faithful, loyal fans to defend it.