I understand the problems but I think there are clear cut cases where /48's make sense- a large scale anycast DNS provider would seem to be a good candidate for a /48 and I would hope it would get routed. Then again that might be the only sensible reason...
f-root does this on the IPv6 side: 2001:500::/48
Whether that's available everywhere on IPv6 networks, is as Bill pointed-out, another question.
<http://www.arin.net/reference/micro_allocations.html> explains what's going on with that /48. <http://www.root-servers.org/> shows some other /48's. if the RIR community wants "critical infrastructure" to use a /48, then f-root's operator will comply. if the RIR community changes its mind, then f-root's operator will comply with that, too. -- Paul Vixie