The Core Duo-based MacBook Pros debuted in January. At the time, Apple CEO Steve Jobs promised the laptops would leave the company's assembly plants in February. Apple's online stores in the UK and the US immediately offered the machines on a pre-order basis and said the computers would ship in "February", as Jobs had pledged.
It seems that even pre-orders could be affected, an unusual situation with such a popular product. If you have ordered a Macbook Pro, you may want to check on your order to find estimated delivery dates. But I suspect that many will feel the improvement in hardware will outweigh the delay in getting their new notebook.