Im a mobile web developer. Its a totally different ball game. The biggest problem with developing for the mobile web is the vast amount of different devices that are going to view your page.

Different screensizes,css implementations (if at all),usually no javascript,older devices using wml (however xhtml-mp seems to be the winner) then there is the dodgy implementation of a lot of the operators wap gateways.

For example Vodafone thought it would be a good idea to strip out the user agent header in http requests, so the one way of serving content appropriately to the device is taken away from you.

At least if you know what phone it is you can transcode images on the fly to serve the best possible for that handset along with modified mark up if required.

But with all the headaches its very interesting to see how things are developing. Its a aspect of web development that is in its infancy at the moment