I would think that if someone was using a smartphone to go to a libary's website, their goal is to search the catalog. With that in mind I took a look at the 23Thing library examples on a Treo smartphone.
Charlotte & Mecklenberg County - A survey showed up on the Treo at the top of the homepage with a button to close it. That was annoying, it took up a lot of the screen, but I was able to scroll down to their page, it was VERY long (on a computer it has lots of navigation areas). The website is not very mobile friendly. After I closed the survey the screen appeared as a big box of gray, scrolling down two screen worths finally got me to the top of the heading. There is just too much going on in their main page for mobile use.
Ann Arbor - took a long time to load as it is very graphic intensive. It too has too much going on for mobile use. I clicked on the catalog link. It too took a long time to load. The search fields were three screen length scrolls down. It's very hard to scroll on a Treo. The book reviews on the bottom of the page are confusing since one can't take it all in easily on a tiny mobile screen. It also must have added to the time it took to load (a few minutes) If I were using a mobile device to search the catalog I'd be very annoyed with all the extra content mucking things up.
Denver Public Library podcasts - Simple clean page, mobile friendly. I was able to download a podcast and later listen to it on the Treo. DPL homepage was much more mobile friendly than the others. A catalog search box appears prominently near the top, on the first screen length. The page rendered a little funny but it was navigable. The rotating banner was annoying, it caused the page to reload repeatedly. If our plan had data charges based on usage I would not be happy.
Seattle Public Library - cleanest of the bunch, easy to find the quick catalog search box. The catalog results page itself took a long time to load and doesn't display well. I had to scroll to the right (most pages on the Treo resize so no right-left scrolling is needed).