No, I never have a problem with flow. Once in a while I'm working on something that I'm not particularly into. I find a good cure for that is to do some research on the area I have to write about. For me, almost everything is interesting once you look at it closely. There are just too many details. One of my problems is deciding what to leave out.
For instance, two years ago I wrote a profile of a guy who owns a vineyard. I interviewed him at length, but he was pretty dull and didn't give me much zing to work with. So I started reading all about running a vineyard, what's involved year-round. I found some guy's online daily diary of running a vineyard and read about six months worth of posts. It was great. He was really hands-on and funny and scared of losing his shirt. Then I interviewed the dull guy again and we had a way better conversation. He gave me some anecdotes and some insights. Of course in the end I had way too much.
I try to write 1000 words a day on my main work. In between doing that I write goofy stuff and e-mail poems to my brother, etc. I don't believe in writer's block. It's just another word for self-censorship. Everyone's thoughts are shaped in language. All you have to do is let them out.