Over two thousand distributions of Linux and BSD. Sound overwhelming? Take a look at the Linux distribution timeline. It can take quite a while to find a distribution there, even a more popular one. It certainly seems complicated, but it isn't nearly as bad as you would think.
First, many are specialized for a certain task, like Clonezilla and Backtrack and are not designed for general desktop use, and of those that are, some are geared toward power users. There are still a lot aimed at beginners, but not nearly as many.
Next, notice that the vast majority of the distributions are based on either Debian, Red Hat or Slackware. If you learn to use those three, (For Red Hat you would learn Fedora or Centos), You will be able to use many features that their children have inherited. Like say, the package manager and the configuration files. But it gets easier than that.
There may be a lot of distros, but the number of Window managers is much less. The two most popular are Gnome and KDE. Learn those and you will be able to use a substantial percentage of distributions. Besides, most major distros give you a choice of Window manager, and nearly all of them let you install new ones from the package manager, so once you find one you like you can use it all the time.
In the same way, applications like Firefox, Rhythmbox, VLC, Gedit and so on are standard throughout most of the Linux world, and can be built manually if necessary.
Although it is easy to use Linux without it, to get the maximum benefit from Linux you need to learn the command line, and the Bash shell is the default, along with a set of standard utilities.
In conclusion, don't be daunted by the amount of Linux distributions. Pick one you like and stick with it, or experiment as much as you like. It isn't nearly as hard as it seems.