Let's think about the ACTUAL timeframe Apple releases MacBook Pros and MacBook Airs on. The MB is a little trickier as it was integrated into aluminum then MBP and the plastic remained. But if we count them all, it's more frequent than MBP and MBA updates.
- Original v 1,1 MBA. Introduced Jan 15, 2008, Merom CPU 1.6/1.8 started shipping Early February, 2008.
- Revision v 2,1 MBA. Penryn C2D 1.6/1.86 and Nvidia 9400m released
October 14 2008 - started shipping Late October 2008.
- Revision v 2,1 MBA. Penryn C2S 1.86/2.13 released June 2, 2009 and started shipping in June 2009.
Date Timeline = 8 months...
- February 2008 to October 2008 = >8 months (a few days more than 8 months)
- October 2008 to June 2009 = <8months (a few days less than 8 months)
MBA Average Timeline = 8 MONTHS! Not ONE YEAR!
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MBP Releases Feb 14, 2006 to June 2, 2009 (40 months) / 6 releases = <7 months.
Early 2006 Feb 14, 2006
Late 2006
Late 2007
Early 2008
Late 2008
Mid 2009 June 2, 2009
MBP Average Timeline = <7 Months! Not one year.
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Guess what... if the MBA is updated at eight months again, it will be updated around the first week of February which isn't yet here.
THERE IS NO HISTORICAL REASON TO BELIEVE IT WILL BE A FULL YEAR BEFORE THE MBA IS UPDATED AGAIN. It could be a full year, but that's NOT what the past has shown us!
I would say one would be getting the absolute WORST VALUE POSSIBLE to buy a new MBA right now. Apple's pricing system allows people to get the BEST POSSIBLE VALUE THE DAY A PRODUCT IS RELEASED. After the release, the value goes down as the technology gets older and older until the next product update is released. Also, the last time the MBA was released it didn't offer much in the way of component updates but it offered a $700 PRICE CUT! I foresee either a bigger update and the same pricing or a smaller update and another smaller price drop. A price drop with the next release wouldn't be nearly $700, but it could be $200 or $300 less for the high end model if it retains a C2D CPU, Nvidia GPU, and 128 GB SSD. Dell just reduced its Adamo offering with a 256GB SSD to $999, so we can assume that prices are dropping fast on the components in these ultraportables.
If you absolutely NEED an MBA, buy it now. If you don't need it, don't buy it now because it's currently a horrible value versus what the value might be with an update or price drop coming very soon. Even if it takes two months, you will most likely get a better CPU, MORE RAM (making the MBA last longer for you as the current 2 GB limit is the factor most list as the reason they will not buy the current MBA), and some additional small changes to great form factor changes is even possible.
Sure, it could take longer before Apple updates the MBA, but it just isn't likely given the current 8 month cycle... it's been a little less than eight months and a little more than 8 months for the last two updates to the MBA. We are just entering that timeframe since the last update. If you wait, you will probably be greatly rewarded.
Even Mac Rumor's own MacBook Air guide states "Buy only if you need it - Approaching the end of a cycle." It also lists the average days between MBA updates as 255 (NOT 365) and states that we're currently at 235 days, thus implying an average update would be 20 days away.