You probably won't know anything until the CES show in January at the earliest. Even then, we are probably a minimum of 6-7 months away from ready availability of next years line and more likely about a year away. So will next year's model be better? Pretty much guaranteed to be. When you reach this time next year and ask the same question, the 2009 models will be temptingly within reach, there's no end in sight.
Just jump in and buy when you feel like you need a new TV, and the features / quality / budget makes sense to you. This model is "good enough" in my opinion, unless you are looking for something specific that this TV lacks.