DynDNS is changing the ToS on their free accounts to make them less appealing, thus encouraging upgrades to their Pro account for $15/year.
Now a Free account holder is required to “log into your account or update your hostname monthly” or their account gets expired, resulting in the hassle of having to setup their dynamic address again.
Previously 5 free domains were allowed, now reduced to 2.
Updated 2011-01-10: confirmed, a DynDNS alias I setup in 2010 no longer resolves.
