This is a maintenance release, only providing bug fixes and no new features.
The complete changelog for version 0.2.4 can be found here.
For Ubuntu users, the updated packages are available from the Highly Explosive PPA.
Arch Linux PKGBUILD recipes are now available from AUR.
If you are not afraid to use a potentially more unstable version, you can select the photoflow-git versions either from the PPA or from AUR. This development versions include all the new features and bug fixes that are being prepared for the next stable release.