One beta user built a script that sells bitcoin in real-time as he swipes his card and tops up his fiat account, effectively making his card "spend bitcoin" :)
that's so cool. have they open sourced this yet?
There is also this BTC debit card available, which could probably be used in conjunction with your service.
https://www.shiftpayments.com/card
As far as the US IRS is concerned, every time he makes a purchase with bitcoin, it is a taxable event where he must declare any gains/loss from the time he purchased the bitcoin. This type of regulation is hindering BTC adoption in the US. BTC also doesn't solve any problems the average person has in a developed country, but that is another story..