I've had two tyres plugged in the past, never had a problem with them after, is there a good reason not to or is it a case of 'rumour has it' or 'my mate down the pub heard about this bloke who........... ?
I think it's the rumour thing, that said I wouldn't want to ride on a plugged tyre on a bike that will be regularly doing over a ton. I have no logic or fact to back that view up though just that tyres and brakes are the only 2 things I won't happily bodge.
That and the fact that tyres aren't designed or testing when they have holes in them, I personally wouldn't want to be going round a long bend at 90 to have the thing pop on me