@Gnomad et al:

A lot of people commissioning voice-overs demand a mysterious form of english known either as 'Neutral' or 'Mid-Atlantic'. I'm not alone in being baffled as to what this could be. Somewhere on Youtube there are a couple of vids purporting to demonstrate 'neutral english'- the speakers are unmistakeably from North America.....Even if someone manages to speak accent-free, pronunciation will always betray them. Just think of that Fred Astaire song,"You say tomato and I say tomato..."
I think many people here have somewhat missed the point. Everyday speech patterns- 'R' between vowels,obtrusive glottal stops,dialect pronunciations etc.- are all fine and good but do not necessarily belong in commercials,newsreels, documentaries etc. Using a 'british' accent in the USA is something out of the ordinary and therefore it's noticeable when things like 'inter-vowel 'Rs' are present. There comes a point where attention has to be paid to enunciation- and this is where I feel some people are either careless or haven't realised just how they speak.
Then again, proper recording studio facilities are no longer essential, a halfways decent mike, 'garage band' and 'music taxi', a fairly pleasant voice and a willingness to work for peanuts are, combined with customers whose only interest is in quick,dirt-cheap v-os, all that's required in too many cases.
As a UK english native speaker voice artist and musician working in Germany I have a perhaps more critical professional ethos when it comes to enunciation. I try to make sure my enunciation ist clear without overdoing it. However, I'm not perfect! Whilst I'm reasonably certain that my v-os are free from 'inter-vowel Rs', I wouldn't necessarily say that about my singing. If I'm talking to another native speaker then my speech is almost certainly littered with 'inter-vowel Rs', glottal stops etc etc.- in other words,boringly normal.