I'm making major changes to one of my sites and I wanted to keep track of Adsense relevance. But frankly before I even started I tended to get far fewer well targeted ads, than historically.
I mostly use Firefox for development so I set up the Google Chrome browser to block all cookies, delete all on exit, etc. This made a huge difference in the ads I saw. No longer seeing at least half the ads selling products and topics I looked into, perhaps months ago!
With this Chrome setup the ads are actually pretty well topically targeted to the site content. Now with this test bed, I feel a little more comfortable making major mods to the site, including how Adsense ads are delivered and placed.
I just wish I could switch off interest based ads. They probably work on average in very large sites, but not on smaller sites.