I upgraded to BDIS2010 some weeks ago and I am lucky not to have any problems with it as some people on here! <touch wood> 
However I have noticed within Thunderbird 2 when you select an email and click the "is spam" button it does not prefix the subject line with the [sPAM] quote. This used to happen in BDIS2009.
I would ask for some help but this is abviously a bug and needs to be resolved by an update.