I just wing it but there are certain ideas sometimes for a post that just come up to me while I'm out there driving or in class, for example. I usually type the concept in my cellphone or something. And when I get home, I fully write about it.
Mine's a bit of a blend. There are many "diary"-like posts that are spur of the moment.. then there's others that I let fester and brew before sitting down to hash them out.
I do a bit of both. Sometimes I'll get an idea, but need to spend some time developing it...especially if it's a review or informational post. Most posts about my personal life though are on the spot.
As others have said, it tends to be a bit of a mixture.
Most of the time I'm in the wing it camp as well, though I will tend to mentally note down things I'm doing or that are interesting that may be suitable things to talk about.
If there is something I consider to be more important I might plan it out a bit more (or type out a big rambling piece and then go over and re-write it, hehe).
Sometimes I just write whatever on my mind and brainstorm without really doing any formal planning but I do plan what I will blog about and then I kind of just go on from there. I do think of what I will but not how I write it.
I do a bit of both. I like to just write what I feel like writing when I sit with my laptop...but I have loads of draft posts (from days where I had too much to write) for days when I either go blank or I'm really busy and don't actually get the time to sit and wing-it!
A little of both. Sometimes I have a really great idea and want to make sure it gets out in higher traffic days because I think others might enjoy it too. Yesterday, I randomly thought about scrunchies and bad American Apparel ads so I cranked out a post on the spot.
A bit of both. But I have so many ideas floating around in my head that sometimes I stop & write them all down and realise I have enough blog material for the next few weeks! My blog isn't really a diary, more a collection of...stuff. Lol. So it's easy to find things to write about. I don't tend to mention the really personal stuff happening in my life. My blog is my happy place so I always try to keep it light-hearted.