Kendall Miller has written an interesting post at the Reliable Systems blog. To summarize, it's not the technology implementation the determines the ultimate scalability of the system but it is the software architecture itself.
This is a recurring theme that I hear time and time again from well researched web systems implementers. In my experience something like 80% or more, of the problems companies will have operationally when trying to scale a system efficiently will trace back to the work and care taken by the developers, software, and systems architects very early on in the projects life cycle. This dramatically effects TCO, Total Cost of Ownership, of a system over time.
I'm not saying scale early necessarily because you don't have to over engineer things like software and infrastructure up front. But, you should be thinking about scalability early in the overall design and systems implementation or you will suffer later. It's just good sense and I think the article written by Kendall Miller and the subsequent comments to the article echoes this as well.
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Original Article: http://kendall.srellim.org/development/technology-is-not-scalable