sorry if i wasn't being clear enought, what i meen is, 1cert to rule them all (no really, just for the admin interface), and SNI for the rest of it.
i would like to have none-sni supporting browers still at least to be able to use the admin interface, while users who dont care so mutch about backwardcompatiblillity can have ssl based websites also (for say joomla's admin interface or stuf like OScommerce.
this however would require some php code (i think) that could manage SNI, and its certs,
i think that ano 2011 not supporting sni is like building a website in ms word '98 it mostly works but its not what you'd expect.
on a client side i would probly write some jscript or php+jscript warning msg that detects ms win xp, and recomends updating to at least firefox 3.6 or upgrading their os to supporting versions.