I have recently seen a number of web sites where you want to click a link in content on the page, but as your mouse moves across an advertisement (ad) to get to the link, the ad expands to cover the content link, and I accidently click the ad often leading me someplace as a user where I DID NOT choose to go.
I find this beyond annoying from a user standpoint and feel it reduces site usability.
I do see the value of ads in web sites :) some revenue helps drive the content existance but golly gosh gee I really don't like this.
What is the best way to handle this as a web site developer?
As a web site developer you can choose ad proveders who don't do these things. Or manage ads by yourself. Or put a "donate" button.
Autoenlarging ad areas could also violate an ad agreement, where the ad's dimmensions are described. Check the agreement text.