But as of today, I don't get paid in BTC, I can't pay for any of my 'standard' expenses (mortgage, utilities, etc.) in BTC, so if I owe my friend $50 and want to cover that electronically, if I use BTC, it's likely he'll end up with something more like $48 (or whatever) if he wants to actually buy something with it, which seems to be approximately the same situation as a "Visa tax", but with less predictability. Your Yen example is a good analog, actually. I also don't pay him in Yen for the same reasons. I don't get paid in it, he can't buy most things with it, and doing so would effectively reduce the amount of money due to conversions.
Frankly, when I'm owed money in the $0-100 range, I generally just ask for an electronic Amazon gift card. It's basically instant, there's no fee or conversion penalty, and we buy enough there that in those sorts of amounts, it's about as liquid an asset as there is. I understand this doesn't further any sort of advance, and perhaps even reverses it, but it's certainly pretty painless. That being said, it's not something I'd want to accept large amounts of with any frequency.
Also, on volatility: As market cap rises, the volatility will necessarily decrease. The "wild 10% swings in a day" phase is just a phase, I wouldn't expect BTC to be more volatile in the future than, say, gold, or any national currency like the Yen (which itself has swung 10% in value in the past 2 weeks). This is because as the market cap rises, it takes more and more capital to influence the price significantly. Right now, any random person with $10,000,000 can cause a swing, whereas if the market cap was 10x higher, it would require ~$100,000,000 to have the same effect in terms of percentage.