My MBA is purely for work - my whole folder of work documents is just under 3Gb - and having transferred all the data and programs that I need, am currently running at 97Gb free from the original 128Gb.
I´m a teacher, so my work folder does steadily increase in size as I make new worksheets, find new videos and accumulate past exam papers, but 97Gb will serve me right for many years to come!
Have an iMac at home to do all the heavy lifting, which shares my iTunes library around the house. I think as long as you know exactly what you are buying the laptop for, the relatively small storage capacity isn´t a problem.