Some feedback: we have been successfully using HE for years at our office, because of a lousy ISP that keeps on piling up ridiculous excuses. Latest one was that we couldn't get IPv6 because we had a "special" IPv4 block.

Also used SixXS but the aiccu+AYIYA/6in4 requirement isn't ideal when you have some network gear that supports 6to4 tunnelling natively.