One problem of the Serendipity 1.7 has been reported to us, that people might be missing proper relative links for i.e. the "Log in to the Blog" sidebar link and missing links in notification emails.
This stems from a change in how Serendipity defines the "URL to blog" variable of your configuration. In some installations, the value for this might be empty - this will most likely happen if you upgraded an older Serendipity version and saved the configuration without entering the URL to the blog in the empty field. It does not affect fresh installations of Serendipity 1.7, and it will also not affect you, if you do NOT change anything in your global serendipity configuration after the upgrade to 1.7.
A proper fix for this will be put in to an upcoming 1.7.1 point release. However to easily fix this before a new release, you can do andy of this:
Enter your blog's configuration, search for the option URL to blog and enter the full URL to your current blog, i.e. http://blog.s9y.org/. If Serendipity runs in a subdirectory, you need to add that path as well, like http://www.example.com/serendipity/. Don't forget the trailing slash as well.
Or you can simply enable the option Autodetect used HTTP-Host. This will make Serendipity auto-detect your blog's domain and path and should work in most of the usual webserver setups.
Or you can fetch our current master from github.com/s9y (the "pending" 1.7.1 release), which contains a fix that will execute an automatic upgrader task to set the "old" configuration option properly. This option is more for advanced users, others should be better off with solution #1 or #2
A second issue that has been reported for 1.7 is that when editing usergroups, the current name of a group can show up empty in the editing interface. You will need to re-enter the proper name of that usergroup before saving. This will also be fixed in the upcoming 1.7.1 release, however it's impact should be low right now.
We are sorry for anyone affected by this issue, but are happy there are easy fixes available for this. Many thanks to Onli from the forums for digging into this issue and committing a fix.