Kind of like Ryder, this name makes me picture a high school movie from 1985. In it, a guy named Slade is the coolest, most attractive, and most popular guy in school. However, if you fast forward 15 years, you see poor Slade working on a gas station or some crap like that. This name doesn't sound very serious or mature, and it sounds like a bit of a pseudonym to replace a nerdy name, kind of like an actor might go by Ryder instead of Clarence. Yes, I made that up, I've never heard of such a case.
Sounds to me like a combination of "sling" and "blade"--like the movie "Sling Blade." (Good movie, though.) But all in all, to me the name Slade implies violence. The only way I can see myself using it is for an evil character.
I have only recently heard the name Slade and I have fallen in love it. It sounds upscale, modern, mysterious, and if I have a son, his name will definitely be Slade.