mickjoebill,
A single engine heli will fly fine in IMC (icing conditions excepted). See SAS's post above.
However, when things start going wrong, it's not very nice place to be. Remember, a single doesn't just have one engine, it's also invariably only got one alternator/generator, one hydraulic system, one pitot/static system ie no system redundancy. If anything breaks, things start getting hairy PDQ.
The bottom line though is that if the engine were to stop in a single whilst over a city/built up area, you
might have a chance to auto to a clear area. If the engine were to stop when you're IMC, who knows what's underneath you?
HTH,
B73