Seth Godin asks 'Is architect a verb?', and makes an interesting distinction between design and architecture (emphases mine):
Design carries a lot of baggage related to aesthetics. We say something is well-designed if it looks good. There are great designs that don't look good, certainly, but it's really easy to get caught up in a bauhaus, white space, font-driven, Ideo-envy way of thinking about design.
So I reserve "architect" to describe the intentional arrangement of design elements to get a certain result. You can architect a computer server set up to make it more efficient. You can architect a train station to get more people per minute through the turnstiles. More interesting, you can architect a business model or a pricing structure to make it far more effective at generating the behavior you're looking for.
Seth's definition of 'architecting' is very closely aligned to what I've termed 'design with intent': strategic design intended to result in certain user behaviour. My definition's a bit narrower, probably, with the focus on influencing user behaviour, techniques for doing that, and the rights and wrongs of it, but there's a big parallel there. The key thing is that both architecting and designing with intent are deliberate (and often deliberative, too, in the Aristotelian sense - thanks to Kristian Tørning for this point). There is some reasoning, some intended outcome, driving them. As we've seen before, not everyone likes the term 'architecture' (or 'architectures') being used outside the pure building and environmental design context. But it's useful because it clearly implies the planned, deliberate nature in a way that, say, 'structure' doesn't necessarily.
Of course, many designers, especially interaction designers, would argue that they always design 'with intent' anyway. They're always 'architecting': considering the relations between system behaviour, user behaviour, users' goals, and so on is the very basis of the human-centred/user-centred turn in design. But that doesn't negate Seth's point: 'design' does have a lot of aesthetic baggage. It may be useful - and persuasive - baggage sometimes, but it can serve to mask what design really is, or what it can be.
Seth's final point draws a number of other aspects together:
Architecture, for me anyway, involves intention, game theory, systems thinking and relentless testing and improvement. Fine with me if you want to call it design, just don't forget to do it.
Based on my research so far, I think we need to add ecological psychology and behavioural economics to that list, at the very least.