Garbz is on the right track Mike.. but Colour Spaces is a bit of a mind-bender and I don't have my head around it fully either.
With Photoshop managing profiles I can convert between files between profiles or open the sRGB exported version of a RAW file and have it all look pretty similar (I don't notice a difference anyway).
However, if I view Adobe RGB images in ACDSee then they look flat, muted etc but that is an ACDSee issue (I might be able to fix if I looked into the settings).
The only time I've ever run into trouble is with my recent images of the bioluminescence.. I hadn't really investigated at the time but I had some out-of-gamut issues.. I think the monitor could not properly display some of the extreme blues in the ProPhotoRGB colour space file, so Photoshop warned me by blacking out those pixels. The sRGB exported images looked fine.
You prompted me to do some more reading and I found this article helpful:
http://dpbestflow.org/color/color-sp...color-profiles
Phil