I tend to dress quite casually - unless there's a good reason to do otherwise I'll be in jeans and a t-shirt, or something similar. I'm comfortable in it and I take the view point that in general people shouldn't be making assumptions based on what I'm wearing. Of course they do, and while this can be infuriating at times it can also be amusing. The man at the RBoS who witnessed me signing the personal DD guarantee form for Black Cat obviously couldn't reconcile my appearance with what I was there to do, for example.
I'd never thought about this from the other side until a few weeks ago. I spoke to someone who explained how difficult it had become to conduct business meetings with other companies with the increased level of business casual. In fact on occasion different branches of the same company that he'd be meeting with would have different dress codes, so he'd go to something involving casual dress in the morning and something with full business suit attire in the afternoon and end up feeling over or under dressed.
This isn't likely to make me change my own behaviour in the immediate future (I don't have to interact with external parties as part of my current job). It did help me realise that there was another explanation for awkward behaviour when I'm my usual scruffy self that wasn't just about judging on appearances though.
(All of the above blatantly obvious once you think about it, but it took that conversation for me to do so.)