Hi,
I have a thesis written using pdflatex as my compiler. However, I just bumped into xelatex for the first time and it looks really good and I want to some of it features. But I am not sure what are the pros and cons of xelatex over pdflatex? I tried compiling my thesis and it compiled without problem, but took a few seconds more than usual.
Any ideas why I should not move to xelatex? And if xelatex is really that great - why is it not that popular? I am using a lots of packages with pdflatex - will they all work fine with xelatex?
Can anyone provide any useful links?
General ⇒ xelatex vs pdflatex
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xelatex vs pdflatex
This link and this one from the TeX stack overflow site should answer most of your questions. With regard to package differences, perhaps this one. (I'll add to that list, however, that the movie15 package doesn't work with XeLaTeX.)
As far as I'm concerned the chief advantage of XeLaTeX is the ability to use system fonts rather than fonts specifically packaged for LaTeX and to access the advanced features of opentype and AAT fonts. If you have no need of those features, then I'd stick with PDFLaTeX. PDFLaTeX is faster than XeLaTeX as you've noticed. It also currently has better support for certain advanced microtypographic features. (Margin kerning and the like.)
And if you really want to confuse yourself, you could also be considering LuaLaTeX at this point too.
As far as I'm concerned the chief advantage of XeLaTeX is the ability to use system fonts rather than fonts specifically packaged for LaTeX and to access the advanced features of opentype and AAT fonts. If you have no need of those features, then I'd stick with PDFLaTeX. PDFLaTeX is faster than XeLaTeX as you've noticed. It also currently has better support for certain advanced microtypographic features. (Margin kerning and the like.)
And if you really want to confuse yourself, you could also be considering LuaLaTeX at this point too.

Re: xelatex vs pdflatex
Note that movie15 has been replaced by the media9 package, which is compatible with xetex:
http://ctan.org/pkg/media9
http://ctan.org/pkg/media9