Google Groups owners have received an email from Google today that details some changes that are going to happen in a few months. And sadly there are no feature additions -- they're all things that Groups will be phasing out.
So, starting in January 2011 you will no longer be able to create or edit customized welcome messages, pages or files. Such content already on your groups will become read-only. By February, these features will be turned off altogether.
Google has created an easy way for you to export all this content into a ZIP archive. You can do so by going to your pages or your files homepage on your groups and clicking Download all pages or Download all files.
As for alternatives, while you clearly won't be able to find one for customizing welcome messages, Google does recommend using Google Sites for page creation and Google Docs for file storage. Pages made in Google Sites and files uploaded to Docs can be shared with the members of your groups. While these solutions probably require a bit more work than the features that are in Groups today, and may not integrate as well with Groups, at least they're still under the Google umbrella -- if that's worth anything to you.