There, I've now got a client that works good enough for me. There are some features that are missing and some spurious bugs that show up from time to time causing either stop in music or death of client. I'm guessing that the mix of threads in GTK+ and Despotify causes this somehow. I'll investigate more some rainy day...

What is it?
A Spotify client based on Despotify, aptly named footify. You need to have a Premium Spotify Account to use it.

What can it do?
+Load playlists and present them in a tree with full kinetic scrolling for browsing.
+Play songs from playlist with updating time and a progress bar.
+Pause and resume playing.
+Load and display cover art.
+Automatically handle start of the next song in the playlist.
+Move to the next song in the playlist.
+Search and display information about songs which is presented with full kinetic scrolling.
+Start songs from the search result.

What can it not do?
-Shuffle. I never use it...
-Repeat. I never use it...
-Offline storage/mode. If Despotify adds this, I might have a look.
-Save settings (like username and password). It's easy to have this compiled into the client.
-Go to previous track. There's a button for it but I never use it.

What special features are there?
+After logging in, the view is changed to the playlist one.
+After picking a song from a playlist or a search, the view is changed to the playing one.

It also turned out to be real easy to modify the source and compile it for my normal Linux machine without Hildon functionality. So, clients for two platforms for the price of one.

Other problems?
-The Despotify version that is in Extras-devel(?) is rev. 488 which is broken (unless the maintainer of that package has updated it). I've compiled my own library using rev. 508 which, potentially, makes my client binary incompatible with the available version.
-It's easy to find things I haven't tested very much and confuse the client.
-I can't say I have completely understood the mechanics of Despotify which might cause some trouble.
-There are some inconsistencies with the state of the Play/Pause button. This is the most boring part of UI programming.