By popular user request, we've now added the ability to sort your leads by date added, so that your current leads show up at the top of the list (or vice versa).
When looking at your leads list, you'll see a new column called Created. You can click this column header to sort your leads by the date they were created.
You can also see when the lead was created right on the lead screen itself. New information has been added to the first lead information tile.