Ah yes the .mac conundrum, translated it is a personal service from Apple for $100 a year, not to be confused with a commercial domain name server.
You will have space with an ID name but no domain identifier. http ://www.customer/mac.com
rather than http ://www.customer.com so your site is not really in the public domain. If all you want is online storage and a place to demonstrate your life at work & play, .mac is a fair offering now with tools and 10 gb’s, but if you want to be listed with google, yahoo, MSN, and so on to display your company and product it is not the option you want. Most ISP's offer space with each account, Earthlink offers 1GB free and additional space at a premium, for example, but like .mac, on earthlink you get http ://www.customer/earthlink.net