BioWare has said you will not be able to play the PC version of Mass Effect without an Internet connection.
This is due to SecuROM copy protection features that try to revalidate your CD key online every 10 days after installation. Miss it and you will not be able to play the game until a successful check is made.
SecuROM, you may remember, was at the heart of authentication problems in the PC version of BioShock.
However, BioWare assures us that EA is "ready and confident there will be no server problems". And if there is, then all the necessary customer support is in place to answer your calls.
Priestly was also keen to point out that previous PC titles Neverwinter Nights, Knights of the Old Republic and Jade Empire all used SecuROM in one form or another, and that this wasn't a product of the recent acquisition by EA.
Pop over to the official Mass Effect PC forum for a full FAQ and the recently released system requirements.
For those wondering, Mass Effect PC will be a conversion rather than a rushed port, featuring improvements such as plenty of hot-key slots, individual squad commands, faster loading times, less texture pop-ups, speedier elevators, and free Bring Down the Sky content.