They just released new Apple models which are faster than the prior notebooks.
However, as Bob Said, Apple will be converting to Intel chips in the near future.
My friend who uses Apple for his photography job and Apple consulting business just bought an Apple 17" powerbook used for $2300 as it is essential for him to use now.
But if an Apple is not essential now it does face an issue with the conversion to a completely different chip family.
Note, however, that IBM PC notebooks are facing an upgrade to Windows Vista and 64 bit computing next year as well.
So, the key thing if you buy a new notebook now is don't overspend (under $1500 for IBM or $2000 for Apple) as you will want a new notebook within 2 years either way (although this notebook would still run longer hopefully as a secondary notebook)