"By submitting User Content to us, simultaneously with such posting you automatically grant to us a worldwide, fully-paid, royalty-free, perpetual, irrevocable, non-exclusive, fully sublicensable, and transferable right and license to use, record, sell, lease, reproduce, distribute, create derivative works based upon (including, without limitation, translations), publicly display, publicly perform, transmit, publish and otherwise exploit the User Content (in whole or in part) as Mumsnet, in its sole discretion, deems appropriate. We may exercise this grant in any format, media or technology now known or later developed for the full term of any copyright that may exist in such User Content."
They've changed just two things from the implied licence and implied terms that they had anyway.
One: they've now made the licence irrevocable. I can't rely on copyright to have this post removed.
Two: they give themselves the right to sub-license the content to others in any form. That allows them to write their mumsnet blogs, publish their mumsnet books, do their joint activities with chosen charitable and political groups and generally be mumsnet and hopefully make a bit of money.
I would humbly submit that in these terms they are not being unreasonable.
BUT!
[they also get me to waive my moral rights that I couldn't face talking about upthread].