When compared against similarly configured PCs, Apple's computers are competitively priced. However, in taking a step back and looking at PCs vs Macs as a whole, Macs are generally more expensive because Apple does not cut many of the corners PC manufacturers do (ie: selling fancy chips with cheap connectivity and casings). With the advent of cheap laptops and netbooks in the PC market, and rumors of Apple exploring netbook options, it's clear Apple is definitely feeling the pressure to serve this portion of the market.
