Web developers who have used CSSEdit are familiar with the simple interface which belies many powerful features. You can expect the same from Espresso. Coda users will be interested as well; when Espresso is feature-complete, you can expect a TUAW-style head-to-head comparison of the two. Personally, I'm a die-hard TextMate user, which any of the TUAW crew can attest to. I always have trouble getting into new editors, no matter how rich their feature set may be. I stopped editing CSS in TextMate when CSSEdit came out, though; there's just no comparison. Knowing CSSEdit the way I do, Espresso may be the platform which finally pulls some of my TextMate loyalty away ... at least for web design.
You can grab the time-limited (30 days) beta from MacRabbit's site. If you're a developer, make sure you check out the wiki. For me, the most appealing aspect of Espresso is its extensibility, and a look through the SDK should pique the interest of any code-sligner.