I've had bad experiences with client-side JSF state saving. Not that I'm doubting you, it's just that for just one form in the application I'm developing, the encoded state information was nine megabytes in size. That's not counting any images or multimedia embedded in the page. For a dial-up user, that would make the app pretty much useless.
Without a way to overcome that limitation, I'm pretty much forced to use server side state saving. :(
9 meg!!! wtf!?
Trinidad has a enhanced version of client side state saving - I haven't tested it with Seam but if it works then it sounds helpful
http://incubator.apache.org/adffaces/devguide/configuration.html#web.xml
If you're interested Gavin, the form that generates such a huge amount of state information can be viewed here...
http://www.gradview.com
Just click the "Register" link at the top of the page. Of course, I'm not using client side state saving, since that's a production site, but you can see that the form really isn't all that big, and it does indeed generate around 9 megs of state information.