Its still in beta, but works pretty well. I've found some problems with UTF8 encoded strings and I have an open ticket on that.
I've released a Perl client library to CPAN, Net::Stitcho. It allows you to use it from your Perl programs easily. Its not feature complete yet, only the send message API is supported, but it should have the signup API today.
Its not clear to me the business model behind Stitcho, and getting this deployed widely enough to make a difference is also a challenge, but I like the concept so lets see how it goes.
Net::Stitcho module is, as of version 0.03, feature complete.