Have been using the SMH10 since shortly after it's release. Great little piece of kit - have one on mine and my wife's helmet - and they've been great. Had one warranty issue with my set which Sena handled painlessly and sent me a replacement, no questions asked.
I haven't been easy on them either, as a matter of fact I was going to Revzilla to buy a new one last night as a piece of plastic had broken off the clamp a few months ago exposing the internal electronics, (my fault, not Sena's) and I figured after nearly four years it was time for a replacement. The unit still works flawlessly (and have ridden it through heavy fog, rain, etc.) but I know it's just a matter of time before the elements win out.
That's when I saw the new SMH20 - I'm gonna try and nurse this one along for a couple more months until the 20 is available. Looks like a nice upgrade to an already solid and proven unit.
BTW I've always ridden with earplugs and can hear the audio from the Sena with zero issue. I often have music piped in and it sounds great, even at speed. I normally don't take phone calls while riding, but have a couple of times - the controls are intuitive and easy to manipulate even with heavy gloves on - and everyone I've talked to on the phone were surprised to learn that I was riding at speed during the conversation. The sound quality is that good.