I welcome any service that promotes email (over more proprietary solutions, be that Facebook Pages or some hosted groupware). That said, for a more technical crowd, your page(s) are a bit light on detail:

1) Do you provide an archive? Can it be public?

And while I usually tell people (based entirely on my intuition rather than actual business experience) to charge more -- where does the 100 members limit come from? Certain types of groups, like alumni from a single subject/course/small business/hobby -- might organically grow past that point. Should they then migrate away from your service?

In general I wish you the best of luck - but for me (not really a target audience) -- I'd like to know how this compares to setting up a Mailman-list, D-lang forum or something along those lines for non-technical users? (Apart from the obvious, and undeniable value-add of you hosting the actual service).