Can I be informed each time someone subscribes?

Yes, you can be notified by email each time someone subscribes.

To do so, enter your email address on the page Subscribers → Settings → General. You will then automatically receive a short message in your mailbox each time someone subscribes.

In your list of subscribers (on the page Subscribers → View) you will also see the date each of them subscribed. By clicking on the column header, you can put your subscribers in chronological or reverse chronological order. This enables you to see which subscribers subscribed for your newsletter recently (or a long time ago).