A 'virtual' mailbox for all your mail. Offer a lot of services, if you don't know much about them. The main service is to scan your letters and email them to you. Lets you have a fixed address even if you move around a lot or plan to be out of the country a while and want to still be able to receive and know what has come in the mail.
Sound great, yea? Problem? Cost is $99 per month, and that is just the basic service. They will also nickel and dime you like a bank or airline if you want to do anything "special".
So, my summary, good product, good customer support, but prices that are just not acceptable for an individual. If you run a profitable small business, then $99 per month may be quite okay, but for a regular joe, the price is just not acceptable.