I am certainly not saying that Apple's Mail is a better product than Thunderbird. For one thing, Mail does not have the capability to save searches as virtual folders like Thunderbird - something I sorely miss (Mail in Tiger will certainly have this feature, I am assured). The other thing that I did not like about Mail was that it was too unobtrusive about new mail notifications. Thunderbird's icon in the dock used to jump up and down merrily whenever I got new mail. Mail quietly updates a red count on the dock icon without any effective notification (yes, I did use the sounds and they are not effective .. get with it !). So I searched the cool macosxhints site for a solution and Voila .... Mail.appetizer ... adds a "notification" preference pane to the Mail preferences and gives a nice floating , transparent and resizable window on the desktop telling me who the mail is from, the subject and a small summary. Cool stuff !! So, I guess that issue is addressed.
Have been using Mail for about a week now and seems to work fine. Will update if I decided to revert to Thunderbird.
[composed and posted with ecto]