Ok, after a bit more reading, including of this thread:

http://talk.maemo.org/showthread.php?t=89285&page=25

it seems My N9 is suffering from an issue where it's not alerting me to updates of software from the Ovi store when available...

It turned out that I couldn't update from Tweetian 1.7.0 to the current version.

I did however successfully uninstall it, and install afresh the current version - 1.8.1

dicksonleong8 thank you very much for a great little application! It is my favourite twitter client on most any platform! My apologies for my misunderstandings.

Two things this event has taught me; check the status of updates at the command line from time to time & Tweetian is a brilliant app that I have become very fond of.