Once upon a time, if a reader were to look in the spec pile, s/he'd find scripts BURSTING with voiceovers. Most of these voiceovers would, indeed, be rubbish. But then a huge proportion of the spec pile was rubbish, so really it was no big deal.
Then voiceovers started disappearing from spec scripts. I'm not sure exactly when this started. perhaps three or four years ago. I think I've perhaps seen five scripts this year with VO. Last year, I saw maybe ten, max. Of course we all know why - his initials are R M - but I think it's a great shame.
Voiceover can be a FANTASTIC tool for revealing character and pushing the story forward. Consider these movies that all feature voiceover:
Stand By Me
The Shawshank Redemption
The Brave One
Ferris Bueller's Day Off
The Princess Bride
The Royal Tenenbaums
Days of Heaven
... Need I go on?!?!?
Voiceover is NOT automatically "lazy writing" -- that's dross. If you want to use voiceover, YOU ABSOLUTELY SHOULD -- as long as it a) reveals character b) pushes the story forward. Oh -- like any other screenwriting device, then.
The only caveat to the above? There are readers out there who have swallowed RM's assertions whole and will write on your reports, "use of voiceover = no good". TAKE A DEEP BREATH when this happens, move on. End of the day, there will always be elements of your script that won't appeal to everyone regardless.
Recognise voiceover for what it is - a calculated risk. But then, most things are in this scriptwriting malarkey, right down to the story you choose.