I'm having the same trouble on my new Transformer Prime running ICS - when starting Spotify the off-line line at the bottom of the screen will blink a few times and then stay - indicating that the app is in offline mode. However, my mobile running ICS (CM9) has no trouble on the same network. I've ran both the official and the preview on the Transformer Prime.
Screen rotation problem here as well, I'm also having the online/offline problem.
All this on Motorola Xoom Wifi (4.0.4).
On my table it actually keeps switching between online and offline, sometimes indefinately, sometimes just a few times until it sticks with offline.
The screen rotation is actually one of the bigger gripes for me, since I usually listen to Spotify when the device is docked, which makes using the app really annoying.
EDIT: I just noticed the thread "Official" new application beta release missing feature and wishlist thread, found here, where it states: "Support for wifi only devices (following discovery today that that lack of an IMEI causes the 'forced offline' issue even when connected to a wifi network)" as well as "Landscape orientation" as few of the things in the wishlist.
So those might be fixed in the release version of the preview app.
I wonder where one should sent these wishes for it to be officially recognized?
"1. Clear the app data. On your Android device: Settings -> Applications -> Manage applications -> Spotify -> Clear data
2. Uninstall Spotify. In the same screen, tap Uninstall
3. Restart device. While you're waiting, go to step 4 (this is the good part).
4. Retrieve your Spotify username and create your device password. This is DIFFERENT than logging in with your Facebook credentials. The Spotify username is really for OTHER devices (Sonos, Squeezebox, TiVo, etc.) but it'll work like a charm in this case too. Get it here: http://www.spotify.com/us/help/faq/devices/connect-devices/
5. Reinstall Spotify on your Android device
6. Log in with your SPOTIFY username (NOT your Facebook username). It will likely be 9 digits.
I have the same issue. It drives me nuts when im driving because im jamming out to a song and it just stops. My iPod was stolen and i use my DROID as an alternative. So this app really needs to get fixed especially if people have purchased it too work! I deserve my premium!