Why do the 6to4-6bone relays work so badly? Is it possible to use anycast 2002:c058:6301:: with XP?

I am using XP and I have tried with the default MS relay,
6to4.ipv6.funet.fi and 6to4.kfu.com and various other relays. I seldom
get to ping to any 3ffe or 2001 addresses. Why? It feels almost like the
public "relays" would just be 6to4 routers with no 6bone connection? Or
is 6bone routing totally screwed up? Or are the IPv6 firewalls stopping
my ICPM packets?

Can I use 2002:c058:6301:: (6to4-6bone relay anycast) with XP? Looks
like not. Setting a 6to4-6bone relay with 

	netsh interface ipv6 6to4 set relay <6to4-6bone relay DNS name>

works fine, which I can verify by looking at the 6to4 default gateway
IPv6 address of ipconfig output, but using a literal 

	netsh interface ipv6 6to4 set relay 2002:c058:6301::

will fail.