I've been building sites in XHTML and CSS for a couple of years, and I wouldn't do it any other way.
There's a learning curve and some browser inconsistencies, but they're easily learned and documented in many places on the Web.
The three most valuable things I've learned are these.
1. Validate your code.
Bad code will break the styles.
2. Use margins rather than padding.
This eliminates a lot of the inconsistencies.
3. Add this snippet to the top of your style sheet: * {margin: 0; padding 0;}.
This levels the playing field by overriding each browser's default styles,
eliminating more inconsistencies.
You will have to define styles for everything, however (p, H1, blockquote, etc.)
If for no other reason, CSS lets you display the same content in many ways.
Check this out to get a feel for the possibilities:
css Zen Garden: The Beauty in CSS Design
Peace