The Edinburgh Festival is obviously a good thing, in that it gives lots of little known artists a chance to perform. However, it is also good for the consumer as you can discover why these little known artists are just that. It's usually because they're rubbish.
My advice for the festival is to book early for the interesting or well known acts which you really want to see. don't bother risking the others. if they ARE good, then they'll be back next year and you'll have heard of them by then on the telly, but 80% of them are rubbish.
There are some really good names for the festival, so be organised to get tickets for them, rather than seeing two bad shows.
Also, the tattoo is as good for scots as tourists alike, and the fireworks concert in the gardens is spectacular, although difficult to get tickets for. it is as much fun to go up one of the hiils in Edinburgh, listen to Forth FM and see the fireworks from there. You get a good view of the city and don't have to put up with all the traffic. Also, it is quite fun as you realise there are people doing the same thing all over the city - you can see camera flashes coming out of the darkness all over.
Please bear in mind this advice on festival acts - I've wasted a lot of money in the past. Plan what you want to see in advance, stick to it and you will not be disappointed.