So you are one of those who think iframes are the worst thing ever and should be banned from all websites?
Do you display any advertisements on your website? Yes? Well, then I have news for you. Changes are big that you use iframes on your own website without knowing.
How I found out about this? By accident. I could not get adsense to work on a page with iframes today (a point for the iframe haters here). The ads would just look weird and misplaced.
Conclusion 1: Never style the "iframe" tag without using classes or id's!
Conclusion 2: Many websites do have iframes without even knowing