I do it, and have done it for a pretty long time. In the vast majority of cases, it's (almost) in the form of sitename@myemailaccount.com - which is usually pretty easy to remember.

If someone was directly targeting me, and had my email address from another site, they could probably figure out what I'd used elsewhere. But if it's just a script running through email addresses harvested from site A, then mine will almost always be irrelevant on site B.

The main reason I use it though is that it's a great way to figure out where spam is coming from. Last week for instance I got a "male enhancement" spam from an email address I've only ever given to scan.co.uk. That addres is now on my block list and I doubt I'll be buying through them again.