I have only been up and running for about a month now but have experienced at least on three occasions where my forum was down for up to 4 hrs. Each time I have rung the server they have admitted there was a problem and each time they fixed the problem within 1 hour. Is this acceptable?

For me, no definately not acceptable. Especially 4 hrs! However alot of the time you get what you pay for, I've atleast 10 different Australian hosts and the one I am happiest with is aussiehost.com

I am actually using http://ehostpros.com. Very stable recently. Plus their service is much more prompt than in the past. Perhaps new management or just continous improvement