Now that since MBP 371 has a pretty powerful core i 5 2.4GHz processor with turbo boost, it should be s small working station at home!
It is.
While the fact is that, the speed of MBA 11.6" is faster than MBP 371 for most of daily tasks, so why bother using MBP provioded that it's way much heavier than MBA? Why don't use MBA and everybody is happier?
The MBA "feels" faster because it's all solid state technology, especially the hard drive, which is flash memory, vs a standard (mechanical) hard drive in the MBP. But the 371 MBP kills any MBA in speed and power with regards to processor, graphics and front side BUS. And you can always install a solid state drive in the MBP to match those "speeds" of the MBA.
As far as use, the MBA is intented for the light-duty user (web browsing, word processor, e-mail, etc.), while the MBP is intended for the medium-heavy duty user (all the light-duty stuff + intensive apps and workloads). Figure out what you use a computer for and see which best serves you. Note that heavy-duty users may benefit with an MBA (or iPad) as a 2nd computer/device, for the light-duty work, reserving the MBP for heavy lifting.
The MBA offers great convenience in the form of light weight, thin portability, and flash memory speed for those daily tasks, i.e. e-mail. The MBP offers a "desktop in the palm of your hands" portable solution. It's a full computer, available in larger screen sizes with i5/i7 processors, lighted keyboard and a hi-res display, which is great to replace the home desktop once and for all.
We will likely see the MBA's features in future Macbooks and Macbook Pros. I think the MBA is Apple's test mule right now, and they'd love to move forward with all solid state and no optical drive type laptops.
Note that, while the MBP may be heavy compared to the MBA, it's actually one of the thinnest and lightest 15" and 17" laptops around.
Seems that the SATA HD drive is to blame for the sucking speed, so where can I replace it with SSD drive? Apple online service don't support that, right?
Search for OWC, newegg.com, Amazon, etc. or your local computer hardware store.