It's a dilemma any/every designer encounters at least once (or in my case, constantly) in their design career - how to create a design that is not too trendy yet still appeals to the current market. At REM we strive to ensure every design we do is custom and best represents the personality of the organization and message they wish to convey, but obviously, there is a lot more thought/strategy "stylistically" that goes into every design we create.
If you look at Apple for example, their software updates seem to give a clue of current trends (although as of recent I am unsure whether they are helping define new trends or are just lucky to jump on the bandwagon early enough for us to not notice). Early releases of their mobile based IOS software had the softer 3-dimensional gradient icons.
This has changed (along with recent trends) to the "flat" style graphic for their icons. This is all well and good for them as they can make software updates as often as they like and affect the look of all user devices to keep them at or ahead of trends stylistically but this isn't realistic for the average website.
An organization can't possibly budget or for that matter, justify updating/redesigning the look of their website bi-yearly to keep with trends. That being said, I can in confidence say that this is just one of the many considerations we think about when designing a client's site. It's a struggle but it guarantees reasonable longevity of the designs we create.