Hi Mawkish and friends,
My two cents...
I wonder if the issue of calling oneself a 'Buddhist' or not, or calling oneself an 'agnostic'/'aetheist' or not, has something to do with questions of honor, status and prestige. I am referring to the sociological concept of 'symbolic capital'. You can look it up on Wikipedia if you like, but by way of example: In addition to the usual factors determining the outcome of a presidential election (i.e. knowledge, expertise, experience), there is also the factor of symbolic status. For example, in the case of Obama it was around the color of his skin, whilst for McCain it was around his past as a war hero.
In contemporary secular societies where there is much distrust and discomfort towards anything remotely 'religious', to call oneself a 'Buddhist' is to potentially diminish status, honor and prestige. It is to lose symbolic capital. By the same token, to call oneself an 'agnostic' or 'atheist' is to potentially boost status, honor and prestige. It is to gain symbolic capital.
Perhaps this is why some people prefer to call themselves 'vipassana practitioners' or 'Zennists'. For after all, vipassana is widely perceived to be non-religious in nature, whilst Zen (having been popularised by the Beat Generation) has a certain artistic and counter-cultural status in the popular imagination. By the same logic, it should be quite obvious why some people prefer to call themselves 'agnostic' and 'atheist' (For academics, given the role and function of educational institutions, it is easy to see why they think of themselves as more 'objective').
As Buddhism takes root in the West, it seems that people are becoming more willing to call themselves 'Buddhist'. In some situations, calling oneself a 'Buddhist' gives one more prestige and attracts less chance of ridicule than calling oneself a 'Christian'. Buddhism, no doubt, is accruing symbolic capital in the West. This manifests in positive and negative ways. We can see how the Dalai Lama is widely revered, or how Buddhist iconography is exploited for commercial purposes.
I agree with TheDhamma that committing oneself as 'Buddhist' can be a good thing as it can encourage progress on the path. However, as I have been trying to suggest with the concept of 'symbolic capital', 'Buddhism' or 'Buddhist' cannot be separated from wider sociocultural dynamics. The concept of 'symbolic capital' clues us in into the way in which individuals grapple with their sense of self, and especially, their sense of self in relation to others.
So, following pink_trike, I would suggest that if one is committing oneself as 'Buddhist', one has a responsibility to be ever mindful of the processes behind the use of such labels. For insofar as Buddhism is committed to selflessness, is this not what being 'Buddhist' demands of us?
Your fellow Buddhist,