I have sort of "unstated" themes for each day on my blog. The only ones I really label are Blog Tips Tuesday and Top 3 Thursday (meme). Otherwise, they are general categories that I post within, such as motherhood, media, kids, etc.
I wrote in one of my "How not to burn out" blog tips Tuesday posts a month or so ago about how I find that themed days helps me come up with topics easier. Helps me from sitting at the computer and thinking "What am I going to talk about today?!" And helps me write about various topics instead of just hitting the same ones over and over again.
Love your ideas!