although the actual release date is unknown. however, after Apple started using Intel chip, product life cycle become more predictable.
Intel will release new Centrino in march this year. which will have core duo 2 with 800fsb. new 965 chipset and Robinson technology. so it is logical to say.. Apple might have new products by June this year.
ps. i think this year is going to be very exciting for Apple. Steve jobs said on the keynotes that "Apple is going to introduce a lot of exciting products in the next few months"