Web 2.0 may not have a clear-cut definition but irrespective of which way you look at it (there are 3 different ways of looking at web 2.0), it is about the behavior of complex system, it is about collective intelligence and it is about emergence. The fundamental principles governing such systems are that the whole is much more than the sum of its parts – the behavior of the system cannot be derived or understood by analyzing individual elements.
Traditional approach to architecting and problem solving is to…
This approach does not work for complex systems
Web 2.0 always deals with complex systems
So when dealing with such systems, as an architect, you need to modify your approach.
Postulate  – Any Web 2.0 success will always be unexpected
If you look at all the big web 2.0 success you will find that all of them (Google, Wikipedia, Facebook, Twitter …) have defied conventional wisdom. The chances are high that your web 2.0 success will happen in an unexpected way.
Must Do #1 – Let the Architecture Evolve
It is impossible to design for the unexpected. Only thing you can do is to move forward incrementally – always adjusting your architecture to the new reality – paying your technical debts regularly.
Must Do #2 – Adopt Agile Methodology
Agile methodology intimately connected to emergence – if you are not into agile don’t even come near web 2.0.
Must Do #3 – Opt for Loose Coupling and Simplicity of Interface
Only loosely coupled system can quickly evolve – only simple interfaces get widely used.
Must Do #4 – Implement Bottom-Up
The trick is to identify small successes – nurture them – adapt your system to help them proliferate.
Must Do #5 – Resist Temptation to Control
We have the inherent urge to control event which does not go according to our plan – but for web 2.0, such events may be the seeds of success.
Postulate  – Web 2.0 – more often than not – is about customer
Chances are high that as an architect you would want to distance yourself from selling & marketing. Unfortunately, web 2.0 is intimately connected with customer (existing & prospective) behavior – and the money for such project is likely to come out of marketing budget.
Must Do #6 – Think Customer Centric
There is clear evidence that improving customer experience can improve customer loyalty – therefore you need to tune the architecture keeping the customer at the centre (not the organization).
Must Do #7 – Learn Marketing Terminology
Marketers have spent their whole carrier trying to understand customer behavior – to architect for web 2.0, not only do you need to understand how traditional marketing works – you also need to understand and speak marketing language.
Postulate  – Underlying technologies of Web 2.0 is changing fast
There always will be hype around new technologies – not all of them will live up to that hype. However, once in a while, a new technology comes in and creates a paradigm shift in how & what we do. When such a thing happens, we call it an Inflection Point – there is a good chance that we are just about to reach one.
Must Do #8 – Design for Multiple Channels
Customers expect logically consistent (not necessarily identical) experience across multiple channels. BTW – Multi-channel is not just smart phone, many other types of devices and appliances are evolving (have you looked at Sixth Sense?). In fact even web is no longer a single channel – you need to look separately at Aggregators, Social Networking Sites, Micro Blogging…
Must Do #9 – Understand Cloud – Especially Google App Engine
In one sense, cloud is just an extension of virtualized hosting solution but 3 distinct cloud strategies are in vogue. However, do look at Google App Engine – though it is still work in progress – it has the potential of altering the economics of IT.
Must Do #10 – Think Beyond RDBMS
Brain cells are in billions but the interconnections are in trillions – our intelligence – collective intelligence of any complex system is derived from the number and quality of interconnections. So, architecting for interconnections is the key to success!