If you have trouble with fonts and character sets, it may be for you: lots of people have the experience that things just work with Xetex which require fiddling with Pdftex. Two capabilities:

• Xetex assumes its input is Unicode. To use Unicode with Pdftex, you need Tex code that manipulates encoding tables, like the {inputenc} Latex package;
• Xetex treats many system fonts, like TTF and OTF, on a par with Tex fonts. Using them is generally no harder than giving the path to the fonts. Pdftex needs to have the font metrics described to it for system fonts. Luatex can figure out this from system fonts, but it's not a perfectly troublefree matter yet.
  

If these aren't issues for you, then there's not much reason to consider moving to Xetex. Pdftex has more sophisticated microtypography.

Look at Joseph Wright's answer to the Differences between LuaTeX, ConTeXt and XeTeX question: Luatex is intended to be the successor project to Pdftex, and he is informative about what is ahead.