Well I've had my Air for a week now and can say... I love it... I also love my MB Pro... So this is how I think they compare...
Air is extremely portable... MB Pro is more of a mobile desktop replacement, a true office on the go. However the MB Pro is 17" and little bulkier, this is the main reason for getting the air.. Easier to use while traveling on business... The Air is usable and fits while in an airplane.
Air has good enough punch for on the go computing. I've ran xCode on the Air, and did some good iPhone development. I was suprirsed at how well it handled development.. But I'm mainly enjoying it as a netbook style substitute.. Browsing the web & IM etc. The MB Pro has awesome performance... I use this for any heavy duty tasks. JEE developmnet, iPhone Development, Photoshop usage, high IO tasks, etc...
Air's battery life is okay.. I'm getting around 3-4 Hours on the charge, but the MB Pro seems to do better (4+ hours)... I
do not have the unibody MB Pro 17", I do wonder if you get the 8 hours as claimed.. The main complaint that I have about the Air's battery life is when I'm in standby... seems to still drain the battery heavily... I don't experience the same behavior on the Pro...
Disk performance... I'm loving the SSD on the Air.. The MacBook Pro has the 7200 rpm... I would say they are pretty comparable... I do notice the writes on the SSD is a little slower than it probably should be... Yeah, this is purely subjective... The reads on SSD are very performant.. It is faster to startup & shutdown the Air than the Pro.
Display... I would say the clear winner on this is the MB Pro.. I'm just way to use to the 17" with 1920 by 1200... The Air is 13.3" with 1280 by 800.. For the purpose of the Air it will fit the bill, but I love the larger resolution... The most noticeable problem is the tool bar on the Air. I think it should/could be smaller.
Form-Factor... The Air is a complete work of Art... I love it... I also love the form-factor of the Pro, but it's definitely for a different need.
I hope these comparisons help people looking at these two machines.... If in doubt, get both
As more things crop up I'll post them...