The MacBook Pro is never going to be an impulse purchase, not for most people, but you can rely on Apple to offer the sort of upgrade options that will make even the well-heeled pause for thought. An 8GB DDR3 upgrade is now available for the notebook, but it'll set you back a cool $1,200.
The kit consists of two 4GB 1066MHz DDR3 SODIMMs and is apparently compatible with the 2.53GHz 2.66GHz and 2.93GHz 15-inch MacBook Pro models. It's only available as a DIY kit; currently the maximum memory you can specify a new 15-inch MacBook Pro with is 4GB. The 17-inch MBP offers 8GB as a $1,000 option.
Alternatively, Corsair 4GB DDR3 RAM is available for $359.99 from Newegg. That's a $480 saving if you really have to have 8GB in your MBP.