I have this problem too.
If I try to add a new text widget it seems to work until I hit save. At that point the count of widgets is incremented but the new widget disappears.
Editing of existing widgets appears to be working, until I hit ‘Save’ at which time all text widgets have only the content they had prior to the edits. I have not yet upgraded to 2.8
All seemed to be working until yesterday. Yesterday I upgraded to Firefox 3.5. However the problem seems to be independent of the browser used – I have tried Chrome & IE7
