Tried to access it today, but it's timing out on me.
$ ping plkr.org
PING plkr.org (65.172.152.98) 56(84) bytes of data.
--- plkr.org ping statistics ---
40 packets transmitted, 0 received, 100% packet loss, time 37994ms
Weird. Still down for me. Tried various traceroutes and they also failed:
USA
http://easynews.com/trace/index.phtml?ip=65.172.152.98
http://www.usc.edu/cgi-bin/traceroute?65.172.152.98
http://www.washington.edu/networking/tools/traceroute?search_address=65.172.152.98&max_hop_value=30&wait_time_value=2&number_query_value=3&number_out_value=3&Submit=Submit&.cgifields=number_out&.cgifields=numeric_address&.cgifields=wait_time&.cgifields=max_hop&.cgifields=number_query
Schweden
http://cgi.student.nada.kth.se/cgi-bin/d97-dho/traceroute?65.172.152.98
http://xyz.pp.se/cgi-bin/trace?t=65.172.152.98
Netherlands
http://www.transip.nl/network/trace.phpx?cmd=traceroute&dest=65.172.152.98
Japan
http://www.tumori.nu/cgi-bin/traceroute.cgi?Host=65.172.152.98&IP=4
Sure it could be the firewall not permitting certain ICMPs, but like I said, I haven't been able to access their Website either.