• Every openly lesbian site has good chances to attract some malicious actions.  Asking for a registration based on a real email address eliminates a lot of that.  It's true that someone very determined could still register and harass us a bit - but it'd be easy to cut them off, and as a bonus it'd take less energy from your admins.
• All lesbians aren't necessarily ready to declare themselves as such in public.  If we leave the site open to all comers, it'll be entirely indexed on google, which meant that the content of every bit of info will be indexed.  We'd like you to be able to announce your birthday bask with detailed address without making this akin to graffiti in a (straight) bar bathroom.  Or to claim participation in an s&m venue without having your parents and your employers find that for the next 10 years.
• Some lesbians would like to offer their services to the public without becoming 100% lesbian establishments.  This is even more true for those of us who work for large companies.  Imagine the mutual pleasure of buying a car, getting your legs waxed, or writing a will among lesbians, without necessarily announcing it to the entire world.  It'd also be very nice to recruit a lesbian for a job in one's company, or to find one for the downstairs appartment, without letting your boss or your landlord know.

So we ask you to register to prevent these kinds of problems.  We hope you'll forgive us in the interest of more participation.  You'll also note that the only info you really need to give us is your email address, you can easily use an alias if you prefer.  It's true that we'll have your address (and please don't use your work one), but if we ever write you it'll likely be to beg you to post more info :-).

 Of course we promise we won't spread your address all over the net or elsewhere.  We're taking every possible measure to ensure site security, and to make sure it's only accessible to the public for which we're building it.