The key components are: Display, Penryn CPU, PC2-5300 RAM, DVD-Burner. I'll do a quick "compare" of top MBP vs a comparable Dell.
Starting with the Dell XPS 1530:
T9500 CPU (2.6Ghz Penryn w/6MB Cache)
1440x900 15.4" Widescreen Display w/Camera
2GB DDR2 RAM @ 667Mhz
250GB 5400RPM Hard Drive
nVidia GeForce 8600 256MB
Wireless N Support
Accidental Damage 1yr
$2,058.00
Compare to the MBP w/2.6Ghz Penryn @ $2,749.00
Deltas/Comments:
MBP - Has 512MB Video Card (over 256MB in Dell) on 2.6Ghz Model
MBP - OS X + iLife, etc. vs Vista Home Premium (You Make The Call)
DELL - Option to go to true HD 1920x1200 Display @ 15.4" (more $$)
MBP - Firewire (You Make The Call)
MBP - Backlit Keyboard (You Make The Call)
MBP - More "Environmentally Friendly" (You Make The Call)
This is also straight up w/o any discounts, tax breaks, educational reductions, refurb, etc... full retail price from both sites.