A few extensions make Thunderbird much faster at doing e-mail. Essentially they allow you to use the keyboard. Check out:-
Quickfile – which allows you to file messages just using the keyboard
Nostalgy – which has a greater range of keyboard shortcuts
There are also more hints and tips about e-mail producivity here, though they are quite e-mail client agnostic, the templates feature referrred to has a Thunderbird parallel in Quicktext another Thunderbird Extension.