Finally version 1.0.0-1 of QSpot is available from extras-devel (and the project garage page), including offline support.. Detailed changelog can be found below:

* Added support for offline mode (i.e., offline synchronisation of playlists). Playlists can be made available offline by longpressing and selecting Set available offline from popup context menu.
* Offline playlists and tracks indicated with different colored icons.
* Added menubar option to force offline mode.
* Offline mode related settings added.
* Last.fm scrobbling updated for offline mode (scrobbles cached in offline mode; sent when going online).
* New French translations added (thanks to Nicolas), and Finnish translations updated (thanks to Tomi).
* Misc. fixes (e.g., problem with no sound in certain circumstances fixed).

In case you have some problems e.g., logging in, try deleting the application settings / cache directory (/home/user/MyDocs/.qspot). Hope you will like the update..