It would be really nice if we could purchase slides of photos here on DPC. I know many galleries and competitions require slides for submission entries.
In the past month I've begun to compete in my local camera club with slides made from digital images. I use a crackerjack local processor, and by using a file of 10 Mg or more, they can make a quite nice slide . I have gotten adequate projectible slides from 6 Mg files; the processor says they now have a superfine film which helps greatly. But yes, it is quite a difference from the nice fat 32Mg (and more) files you get with film.
I've had slides made from my files. In a way, John is right. They do stand out like a sore thumb. The colors are much better than typical slides. That was partly due to the style of photography I partake in versus what my local camera club members shoot. I thought they looked very good actually. I suppose part of that is where you have them done at too.
8-32mb uncompressed size should get you a decent photographic-quality slide. The shop needs to be set up for photographic slides, not just presentation slides.