I seem to have a bit of a thing for tiny computers, so I have my 2009 Air paired up with an early 2009 mini. I love the Air because it is so light, I can (and need to) carry it around with me all day, every day, everywhere I go, but is still an extraordinarily fast, powerful machine. The OWC SSD makes all the difference. I love the mini because it is silent, cool-running, and still plenty powerful. Honestly, as much as people while about the C2D being 'old' tech, the 9400M being worthless nowadays, I find the pair of them to make for a rather zippy machine. I can easily see myself using the mini for another two years or so (it already has just a few days shy of two years under its belt with me, bought it the day after the 9400M minis came out), especially with the 8GB of RAM I have in it, and the Air should last me about the same amount of time at the minimum. The mini is fast because it rarely hits any serious swap anymore, and the Air is because when it does hit swap (and being a development machine with 2GB of RAM, it regularly does), the SSD is so blindingly fast as not to notice any major slowdown.
I also have an iPad that I bring around with me most places, and an iPhone that's always with me.