Flashbacks

A flashback in the middle of an action scene can slow things down and annoy the reader. However, after an action scene, during the recovery scene, a flashback can help develop character and plot. For example, you have a scene where the character fights a man and notices he has a strange tattoo. After the man gets away, there is a flashback to when the character witnessed a man with that tattoo killing someone. The flashback isn't during the action scene, but during the recovery scene.

I like them and have used them myself in one novel. They have to be relevant to the plot though, and make sense appearing in the narrative where they do.

You can go the flashback route, or you do what in my mind is even more annoying, that is info dumping through dialogue. I have no problem with flashbacks. It's another tool in my toolbox. It's certainly not something that you need to pull out on a regular basis, but its nice to know it's in there when it's the right tool for the job.

As to what kind, I like them as the beginning scene of a chapter. I do avoid opening a book with one, as that seems to be particularly offensive to most people (mostly other writers). Scatter them about judiciously and don't let them be overly long. Given those parameters I have absolutely not adverse reactions to them.

I'm not a big fan of flashbacks, but they work if they are well done and essential to the story.

Sure, I've used flashbacks before but not often. I like when back story, which is what is used in flashbacks, comes out in dialogue or in the actions and reactions of the character.