I'd like it if Linode had something like
Hurricane Electric's looking glass, which could ping, traceroute and mtr arbitrary hostnames/IPs over IPv4 and IPv6 from each of Linode's data centers (with bonus toggle to enable/disable rDNS lookups, of course). Personally, I don't care about the BGP-related features, but I suppose other people might find them useful too.
I know linbot has the !mtr commands, but they're user-run, so typically one of them's down for some reason, and another has broken IPv6 or something. Plus, they currently only give a one-line summary instead of the full output. (Which could obviously be changed, but it hasn't been yet, and it would probably take a while.)
<3