I use the MBA 2.13 GHz with 128 GB Runcore SSD as my primary Mac. The rev B/C V 2,1 MBA with an SSD is plenty of Mac to use as a primary computer. I connect mine to a 24" LED backlit ACD at the desk. Leave the USB external SuperDrive plugged into the USB hub of the ACD. The ACD has built in speakers, webcam, and even recharges the MBA. A BluTooth Wireless Apple Keyboard and new Magic Mouse make the perfect complete desktop solution.
The SSD makes the MBA feel much faster than anyone could imagine from an ultraportable. On the go it's an amazing Mac with brilliant display, full keyboard, weighs and takes the same space as a few magazines in your tote. Connect to an AirPort Extreme or Time Capsule at home while on your own wireless network at home for backups and secondary drives. Need to connect from your favorite book store or office - you can access the drive from your home network in the Time Capsule or attached to AirPort Extreme remotely via the Internet.
Need more CPU clock speed? The MBA is a Penryn CPU with dual cores at up to 2.13 GHz... that's fast enough for most people. Need more RAM? Maybe not with an SSD swap files are a snap at upwards of 10x faster than an HDD accesses them. Even when considering RAM needs the SSD factors in.
The Nvidia GPU paired with Penryn Core 2 Duo CPU is powerful and more... all in a tiny little form factor that's lightweight yet stunning to look at with full 13.3" LED display. Add some apps that take advantage of OpenCL and Grand Central Dispatch in Snow Leopard and it's an even more worthy Mac.
It all comes down to what you truly NEED. Most people WANT more power, but I would guess 85% of Mac users would experience faster computing use of the MBA with SSD than an MBP running at 2.66 GHz with 4 GB RAM and a 7200 rpm Western Digital HDD.
Sometimes I think I need more power as it's an easy mindtrap to get into. The truth is the 1.86/SSD Penryn/Nvidia MBA is plenty of Mac to be most Mac users Primary computer.*
Want to boost the speed further? Add a Runcore aftermarket 128 GB SSD and make the MBA even faster with up to triple read speed of stock SSD and fifteen times the read speed of a 4200rpm stock HDD!
I know professors, consultants, attorneys, grad students, business executives, and even ENGINEERS who use the MBA v 2,1 as their primary Mac! If they can why cannot you?
You can definitely watch YouTube or even HD videos on iTunes or Quicktime with the MBA with SSD. I recommend a rev B at 1.86 GHz or C at 2.13 GHz for video performance. Flash and QuickTime hit the CPU pretty hard. With a 1.86/2.13 GHz Penryn video is good on the MBA's native display and even better on the 24" LED Apple Cinema Display! Remember too that Snow Leopard and Quicktime X use h.264 hardware decoding with Nvidia 9400m to provide better playback of video on the MBA!
Best wishes with whatever Mac you get!
* results not similar for an original MBA, 1.6 GHz CPU, nor any MBA with HDD. Apple has allowed MB like performance from this ultraportable by using a low voltage SL9600 Penryn CPU (6 MB L2 cache), Nvidia 9400m GPU, SATA-II SSD, 1066 MHz DDR3 RAM, and cooling heatsink like construction of aluminum unibody.