I bought the Sigma 150-500 this spring, and all in all I am happy. It is the best tele I have owned, and I like the flexibility of the 150-500 span.
On the down side, it is HEAVY - I have just been on a trip to the US where I wanted to bring it but had to opt out because of weight. Ergonomics are good though, and shooting hand held is a realistic option in many situations in spite of the weight. Also, I am female and just 1.64m tall - if you are a huge male Norvegicus specimen, weight might be less of an issue for you, except in cabin baggage situations.
[Edit: Forgot to say welcome to the forum, frodemin - welcome to the forum! Always good to have more Scandinavians! I hang out at the Norwegian camera site akam once in a while, are you there under another usename maybe?]