While I read Feeling Very Strange, I tried to but my finger on the exact definition of slipstream. To my dismay, every time I thought I found an over-arching connection, a new story I read wouldn't have that same trope used in the previous stories.
The introduction of the anthology discusses Bruce Sterling's definition, the person to coin the term. I found a copy of the article while doing my internet search: "Slipstream". Sterling states: "Instead, this is a kind of writing which simply makes you feel very strange; the way that living in the late twentieth century makes you feel, if you are a person of a certain sensibility."
Now, I will admit that some of the stories in the anthology felt strange to me, but not all of them. I truly think slipstream is hard to define, even with Sterling's definition, due to the fact that it's ever-changing. The "stream" in the term could refer to something that keeps flowing and changing. I think that slipstream is whatever fiction at the time that doesn't seem to fit into the normal genre guidelines. What is considered slipstream one decade may be different than what's considered slipstream in another decade. Perhaps, in time, all of the stories in Feeling Very Strange will no longer be looked upon as slipstream, but will be considered the norm for other genres and sub-genres.
There was one theme that I saw in most, but not all, of the stories. It seemed to me that these stories weren't written with simple reading enjoyment in mind, but that each story had an underlying message. They leaned toward the literary side of things, in most cases, and there were a couple of stories that were lost on me because I felt I should be reading between the lines, but unsure of what I was actually supposed to find there.
A few links I found in my searches:
The Best of Slipstream Stories - They even mention in the intro of this that "Slipstream usually has a 'literary' feel to it. The authors take risks with style. Often there is a 'message.'"
Is Slipstream Just a Fancy Word for Voice? - Interesting take on whether slipstream should even be considered a genre, but instead a style or voice.
Slipstream 101 - Another good rundown of the genre.
What's Your Favorite Slipstream Story? - This was a thread in the SF Signal archives. Someone on the thread labeled Spin as slipstream!
NEXT UP: A look at Down and Out in the Magic Kingdom.