The code in mkinitrd for finding net devices won't work for drivers which don't have modaliases (aka Xen, and probably also some of the wacky platform net devices too). I'll probably put in a hack for now for Xen, but we probably want a better fix for fc6 final
Run ethtool -i <interface> and awk out the 'driver' field? (and beat drivers that don't support that...)
Sounds sane... we could actually probably even do a combination of the two. Try the modalias first (because that will better handle if a driver changes names from one kernel to another) and if that fails go for ethtool ops.
Added in CVS. Not built.