Washington law defines a "business pursuit" as an activity that is (1) conducted on a regular and continuous basis; and (2) profit-motivated. Stuart v. Am. States Ins. Co., 953 P.2d 462, 465 (Wa. 1998). CMLP has identified no Washington cases interpreting this test in the context of online publishing out of the home (or elsewhere).
As a general matter, however, Washington courts give this test a broad interpretation. In order to be deemed a business pursuit, an activity does not need to be one's sole source of income and does not need to be full-time, nor does the activity need to be motivated solely by profit. "Some" profit motivation is sufficient to make an activity a business pursuit, so long as it is conducted on a regular and continuous basis. See, e.g., Stoughton v. Mutual of Enumclaw, 810 P.2d 80 (Wash. App. 1991).
Therefore, if you live in Washington, you may be in danger of losing coverage for your online publishing activities if you intend to make a profit from your website or blog, such as through advertisements or a tip jar, unless your activities are temporary or sporadic.
Note that specific language in a policy might lead a court to a result different from the overall trend.