Why would anyone want to join the Euro? Hasn't the past few years shown you that maintaining control of your own interest rates is hugely beneficial? Economies across Europe are just fair too different to have one rate. Germany and France probably wish they'd never said yes after Ireland and Greece!
Well there will come a point where it will be good for British businesses to trade in the Euro though I accept that point hasn't come yet as our economy isn't mature enough yet. Greece should never have been allowed to join the Euro - they didn't meet the entry qualifications and they lied about their national finances. The lesson here is the importance of sticking to the rules, something I feel the British government could be leading on in Europe.
It's probably also worth mentioning that the only reason why Greece didn't go bankrupt earlier, and why Ireland is still able to borrow money is because of the Euro.