I haven't worn a suit to an interview in more than a decade. Times have changed.
Whenever I have a candidate come in for an interview wearing a suit, they look like they're trying way, way too hard - and then the way they conduct themselves in the interview comes across the same way.
If you're not interviewing for an upper management position, I would skip the suit. Nothing wrong with the plaid shirt, even with a tie.
Really, it depends on the industry (tech is a lot more informal than say a well known legal firm on the East Coast), the actual position, the grade - (management, and if so, what level?), the company's corporate culture, and the actual geographical location (I suspect that different regions of the US have strikingly differing traditions in this regard).
Re plaid, or checked pattern shirts, while I, personally, rather like them, I don't see them as interview material (unless you are already on first name terms with your interviewer); rather, I see them as something you wear on a day you wish to show how comfortable an stylish you can be some time after you have been offered the job.
On that topic, I think that vrDrew wrote an excellent post. Tattersal or windowpane or classic stripes can look superb - especially with a smart navy suit and matching tie.