Fedora 31 Silverblue
I am using Fedora Silverblue for the last five months. I started with it just after Fedora 30 was released. So upgrading to Fedora 31 was my first release upgrade with Silverblue. And I must say it was a very pleasant experience.

You can probably upgrade your Silverblue via Gnome Software but I don't like this way because usually it's not very informative about potential problems. So I used the good old way and upgraded via the terminal.
Basically four steps should be enough:
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Verify that you already have the remote for Fedora 31:
$ ostree remote refs fedora | grep "31/x86_64/silverblue" fedora:fedora/31/x86_64/silverblue
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Import a new GPG key for new release:
sudo ostree remote gpg-import fedora -k /etc/pki/rpm-gpg/RPM-GPG-KEY-fedora-31-x86_64
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Rebase to new release:
rpm-ostree rebase fedora:fedora/31/x86_64/silverblue
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And reboot of course.
Workstation will reboot really quickly because the upgrade is already done.
My problems
I had two problems. My first problem was with some external repository that didn't have Fedora 31 packages so I needed to disable them manually (change enabled=1 to enabled=0 in particular /etc/yum.repos.d/REPOSITORY.repo).
My second problem was with RPM fusion (OK, it's also an external repository) which was installed as LocalPackages. Eventually I uninstalled all packages from it and also the repositories. Maybe there is a better way but this worked for me and it wasn't really difficult:
rpm-ostree uninstall chromium-libs-media-freeworld compat-ffmpeg28 unrar rpm-ostree uninstall rpmfusion-free-release-30-1.noarch rpmfusion-nonfree-release-30-1.noarch systemctl reboot rpm-ostree install https://download1.rpmfusion.org/free/fedora/rpmfusion-free-release-31.noarch.rpm https://download1.rpmfusion.org/nonfree/fedora/rpmfusion-nonfree-release-31.noarch.rpm rpm-ostree install chromium-libs-media-freeworld compat-ffmpeg28 unrar
Conclusion
I was surprised how easy the upgrade was and I could work until the final reboot which is great. I felt like having the upgrade more under my control and of course I can rollback to Fedora 30 if something is broken for me.
Good job team Silverblue!
Standard Upgrade
I also did standard upgrade on my second non-silverblue machine. The rebooting/upgrading phase (when you cannot use the machine) took something like 30 minutes. And I had some problems with newer kernel (but it might have been related to some experiments which I did on the machine). But I have to say that Silverblue upgrade was much easier and quicker.
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Image source: fedoramagazine.org ↩