I've been a freelance PPC advertiser for almost 8 years now and I've set up conversion tracking and campaigns for countless different clients and types of websites.
One of my biggest pet peeves? Listing email addresses on the site.
I understand why clients do it. They just want to make it easier for leads or customers to get in contact.
For someone like myself, that relies on accurate conversion data to optimize PPC ad campaigns, it presents a small problem. We can only track 'clicks' on the email address hyperlink (if it's even hyperlinked). We can't track actual email submissions as a conversion nor can we track visitors who simply copy and paste the email address into their email client.
In other words, listing an email address on the site results in some 'leakage'; leads that can't be attributed back to an ad campaign or traffic source. The reason this is a problem is because we can't improve upon anything we're not accurately tracking.
With that said, this issue of listing email addresses on the site is a fairly small problem since most conversions still happen via phone call or form submission for these local lead gen campaigns. But of course I don't know for sure we can't track it; hence the annoyance!