I'm writing this with a throwaway account, for obvious reasons; if this is inappropriate or runs counter to the rules of the site in some way, please let me know.
I'm an undergraduate student in the UK, and am planning on applying to PhD programs next year. For context, I'm looking primarily at programs in the US, and am hoping to specialize in applications of model theory to algebra and geometry. For the past year or so, I have been a reasonably active contributor on math.SE; at present I am self-studying some material, and so have been asking occasional questions when getting stuck on a proof or exercise in the textbook I'm reading, but for the most part I enjoy answering questions on the site, generally in algebra or logic. (I'll avoid specificity, again for obvious reasons.) Most of the questions I've answered are pretty standard, with a handful of (at least for me) less obvious ones, but my activity on the site has been largely well-received, at least as far as I can tell.
So, in short, my question is whether a stackexchange profile can be a worthwhile inclusion in graduate school applications. I see a few pros and cons; on the one hand, I'm (embarrassingly) a bit proud of my contributions here! I really enjoy sharing my love of math and helping people resolve questions (teaching is one of the things I'm most excited for in the future), especially questions that are particularly interesting or thought-provoking. I also enjoy mathematical writing, and one of my favorite parts of the site is that it's an excellent venue for sharpening one's expository abilities. These are important things to me, and I feel that including the math.SE profile in an application would be a good way of indicating this. I also believe (read: hope) that the questions I've posted are worthwhile, and indicate a good understanding of and level of thought about the material I'm studying.
On the other hand, I'm concerned an application committee might see the time spent on the site as frivolous or wasted, somehow; the site is certainly a source of procrastination for me, and my involvement may give an undesirable impression of being too vested in virtual things. Furthermore, while I'm generally happy with my contributions to the site, I'm also aware that one's own view of such things may be very different than the view of an experienced mathematician; what if my answers seem overcomplicated or my questions seem silly?
In any case, these are some of the things I've been thinking about; any thoughts would be greatly appreciated.