yes, good to hear if someone can help compare this, I used a mbp 13" before and now with a mba, the 15in looks good esp in mail/outlook, though I need some time to get used to this resolutions.
Or you could do the math yourself. MBP15: 15.4" diagonal, 1600x1050 display, MBA13: 13.3" diagonal, 1440x900.
Since c^2=a^2+b^2 and you know a & b, then easily figure out pixels per inch = (sqrt(a^2+b^2))/diagonal) where diagonal=13.3, a=1440, b=900 for the MBA13 and diagonal=15.4, a=1600, b=1050 for the MBP15 hires.