It's not that the ads are, normally, annoying. Some may move more around more than others, but they don't flash or play videos (the most evil of evils).
Simviation has mostly non-intrusive ads.
For me, it's an irritation that no matter where you go, the advertisers are following you. From one site to the next.
Think of this, Paul - You go to your apothecary for hemorrhoid cream so you can ride your motorcycle to Sainsbury's.
Sainsbury's keeps track of your online searches and gives you a coupon for hemorrhoid cream.
Sainsbury's sells your shopping list to anyone who wants to buy it. NHS buys it, and notices that you've been buying too many foods with too much cholesterol.
NOW you're in trouble.
How do I know all that about you?
Because I bought Sainsbury's and NHS lists.