You can learn CSS fairly quickly; that's not the problem. It's a bit more complex than old-fashioned HTML, but not vastly so.
The problem is that there are popular browsers (I'm looking at you, Internet Explorer!) that have very serious bugs in the way they interpret CSS, and don't even come close to following the CSS standard. A page written in perfect, 100% flawless CSS is likely to be garbled, or even totally unreadable, in Explorer. That's one of Microsoft's little gifts to the World Wide Web.
What's worse is that different versions of Explorer render the exact same CSS in different ways! You can write a piece of CSS, and it will look different in Explorer 6, Explorer 7, and Explorer 8. So for that reason, if you do a lot of CSS, what you end up doing is writing code that looks at the browser the user is using, and then gives one set of CSS to all browsers except Explorer and then different bits of CSS to the browser if it's Explorer 6, still different bits if it's Explorer 7, and different bits again if it's Explorer 8.
The most maddening, infuriating part of writing CSS isn't learning it and isn't coding it...it's making the site work in Internet Explorer. Creating workarounds and fixes to Explorer's broken CSS rendering can easily take twice as long as writing the CSS to begin with, which is one of the reasons I still use old-fashioned HTML in most of what I do.
