Heres a few reasons.
.... because it is a great outlet for my ramblings and thoughts (and I cant afford a shrink to talk to)
.... to stay sane (read previous reason)
....to keep me in the habit of writing and help me develop my writing skills (i will write a novel one day, no really, i will)
....because I enjoy reading other peoples comments on my writing (Its nice to know other people care or at least are mildly amused by my posts)
Why do you blog?