I've experimented with a lot of different stuff in my email signature, and have settled on this:
It's not perfect, but it gets the job done. I personally don't care for images as they're not usually downloaded by default, for security reasons. And when they're not downloaded, then you get the dreaded broken image indicator in your email and it looks sloppy.
And you have no control over the kind of email client your recipient uses. If they only use email in plain-text form, then it wouldn't show up at all.
I know different folks have different opinions, but I don't like images in email signatures, but that's just my opinion.
I agree, the other thing it can do is make it look like every e-mail you send has an attachment (if you embed the image), and that can be VERY annoying for recipients "trying to look for that file someone sent me."
That depends on the picture? :)
I think it is a great idea. It will create a personal touch and helps to keep you on the mind of those you are emailing.
I like the idea of it, but I think it may not always look the way you want it to when someone opens the email. I saw this happen last night in an email I opened on my iphone. Mobile devices may be especially troublesome for this.