Can Ubuntu or Fedora really replace Windows?

I don't think any Linux distro will ever replace Windows. Not in this lifetime perhaps. There are over 90% of computers using Windows and not even 5 per cent of that are using Linux. Mac OS X is also far from replacing Windows. This is because of the availability of software intended for Windows only. Have you ever heard of a true Adobe Photoshop, Adobe Premier, or Sony Vegas Pro version for Linux? There may be alternatives but they are still far from having the same features. As for which of the two is better, I think Ubuntu is better than Fedora, but Mint is a lot better than the two.

If you are not into PC-gaming, yes. Fedora is using more cutting edge technologies than Ubuntu and Linux Mint, and is directed more towards advanced users. Fedora is more principal on using "free" software (free as in speech). This means that fedora is a bit more reluctant to install "closed" software (for example flash, or a nvidia proprietary display driver, multimedia codecs). It is not difficult, but you'd have to to a bit more effort to have your pc ready for all uses that you might have taken for granted in the past. The main fedora is using gnome3. I'm not a huge fan of that. Fortunately they provide also KDE, XFCE and LXDE spins. The current XFCE 4.8 is already in Fedora 16. Although it is not at the level of gnome2 yet I like it alot. There are a lot of other spins in Fedora: http://spins.fedoraproject.org/ Ubuntu is targeted towards giving the best everyday experience. It is not cutting edge like fedora, but it gives you the option to install the necessary "closed" software ready when you install the system. Also ubuntu has the largest user base among the linux distro's, which results in a stronger support forum and more things working out the box. If you don't like Unity try XFCE (Xubuntu). With Linux Mint you have the advantage that at installation you don't even have to select the option to have the "closed" software installed. A lot of stuff will be working out of the box. However, I find ubuntu always of a higher quality level than Mint.

Linux fans have been saying it's going to be the next big thing after Windows for the last 15 years. It hasn't happened yet. Maybe you don't remember the big deal that some people made when Ubuntu got 50% of the Linux desktop share, which meant it got 1% of the desktop share, a couple of years ago? It was pretty embarrassing, even for some of us who've been using one version or other of Linux for the last 10 years or so. Interestingly, the biggest advance to the market place by Linux hasn't been on computers at all but on smart phones and tablets. Most of the users of those don't give a damn what they are running so long as it works. I expect a lot of the users don't even know they are running Linux, just something made by Google. I prefer Fedora to Ubuntu but that's just my personal preference. You can get and try all sorts of Linux distros, including Ubuntu and Fedora, using a LiveCD - http://livecdlist.com/

No. It's a different system. I can do many of the same things, but don't expect it to be a drop in replacement. Yes. Depends on what you want to do. Both have liveCD's , try them out first.

There's 300 distros, so try a few until you like one best. Mint Cinnamon is my favorite, Bodhi is nice too. I ran windows last summer, because I had a nice OCR program, but for everything else i use linux. Editing movies, graphics, video phone, Arduino programming electronic schematics and simulation, webpage editing.