It seems like everyone has smart phones and other devices that can access the web these days. Is your website ready to be viewed in mobile format? If you're not sure, try this mobile phone emulator and this iPad emulator. Most websites can get away with being viewed on an iPad, but phones can be problematic if a style sheet for mobile devices hasn't been added.
If you were less than satisfied with the way your site looked on either platform, don't worry, it's a fairly easy fix. How urgent is this change? I think it's a good idea to stay up on technology, but the urgency depends on your site. If you already have your site hooked up to Google Analytics or some other analytic system, it's pretty easy to see what kind of traffic you have from mobile devices. I have clients with 20% of their visitors from mobile devices and clients with 1% from mobile devices. Clients with a physical location and phone number will generally get more traffic from mobile device customers who need to find them, but some sites will also get traffic from people researching on the fly or reading articles to pass the time away.
In the end, going mobile is a good idea both to stay current on technology and to help your search engine rankings. The immediacy, however, is all up to you.