The bright side about not waiting:
1. If the model is several months old, most of the bugs have been worked out.
2. If Apple releases something new in the next 10 days and you purchase from one of their stores, they will replace what you bought frequently at no extra charge with the equivalent priced model. Read their pricing policy here:
http://store.apple.com/Catalog/US/Images/salespolicies.html#Apple Prices
Should Apple reduce its price on any shipped product within 10 calendar days of shipment, you may contact Apple Sales Support at 1-800-676-2775 to request a refund or credit of the difference between the price you were charged and the current selling price._ To receive the refund or credit you must contact Apple within 14 business days of shipment.
Frequently they will even delay shipment of your product until the new model is released if it is close enough to that release date.
3. New models probably will have eccentricities which have not been debugged by others leaving you as a beta tester, though AppleCare does cover you for both hardware and software free of charge for the first 90 days, and hardware for the first year. If you decide to purchase AppleCare, it extends both to 3 years.
4. Buying now means that you will get the use of the product that you wouldn't have gotten if you waited. Every day you get to use the product is another day that the total cost of ownership goes down.
5. Shopping around you can frequently find better prices:
http://www.macprices.com/
and if you are really adventurous check these used and refurbished Mac shops:
http://www.macmaps.com/usedrefurbished.html
Oh and never buy the free extra RAM from vendors. Only buy RAM from vendors who back their RAM 100%:
http://www.macmaps.com/Macosxspeed.html#RAM
Otherwise you may find yourself with kernel panics which are a pain to diagnose:
http://www.macmaps.com/kernelpanic.html
6. The only reason to wait is that if you have already tried the current model and nothing you do can make it meet your needs. Ask around though to find out if you may have missed something that could have helped you. I have posted this page so you can find compatible hardware and software:
http://www.macmaps.com/macosxnative.html