It seems to simply be a problem with "mirror.technicpack.net". I wonder if it's overloaded? I'm showing a sudden jump in latency between it and the previous hop (60ms vs. 360ms), and a lot of retransmissions (via tcpdump).
The really annoying thing is, if the client can't contact mirror.technicpack.net, it claims it "Could not connect to minecraft.net", even though it never actually tries. (So blocking it from connecting to mirror.technicpack.net makes it launch faster, but always in offline mode.)
Restarting the client several times helps, because there's a chance it'll actually work. However, even when it does seem to work, sometimes I still end up offline in-game. (Millenaire calls me "Player" instead of my Minecraft account name.)