I have an interview tomorrow. I planned to wear a full suit. The CEO just emailed me that 'the dress code is fairly casual… jeans and a button down shirt… wanted to make the dress code clear so people don’t show up in a suit and fell over dressed."
It’s an interview… shouldn’t I wear a suit?
Go Business Casual. A nice pair of pants and a collared shirt (tie is optional). Take a Coat/Jacket if weather indicates one would be needed. But I definitely wouldn’t wear a full suit in that situation.
I got tricked once… I went to an interview w/ casual clothes and be hold…there are other candidates in suits! Needless to say I didn’t get the job…not sure if’s related to my dress code or not. I’d say wear a suit as it’s better to overdress then underdressed.
Ooh. Bad idea, especially when the CEO called him to tell him about the dress code. If he/she specifically tells you what the dress code is, that’s a test in and of itself. Are you listening? Are you capable of adapting?
I worked for a large contracting firm in the late 90’s/early 00’s. They had a style guide for their consultants which recommended to appear for work and/or interviews dressed “one step higher” than the clients environment. The thought process was that the same level (especially when business casual) was you considered yourself and equal already - not necessarily a good impression when looking to get a job. Too over dressed also caused issues because you were putting yourself “above” the customer and thought you were better than them - not necessarily the truth, but it’s all about perception.
So @sessions, I would suggest you listen to the CEO. If you feel uncomfortable going in jeans, then go in a pair of slacks and a button down shirt (a more traditional business casual). That keeps you looking similar to them, and shows you did listen to what they said.
According to me, there is no need to wear suit for an interview. It is important for any person to look formal by wearing semi formal clothing. However, remember that one should present his or her with full confidence.
I agree with Dave, it is SEO ask you to do,
sorry, SEO should be CEO, 
Sessions,
I would tend to also agree with Dave. While I have always thought it was sort of lame for employers to do little mind games with candidates, you should just do the logical thing and listen to what he says. If you show up and it was some kind of trick and you should have worn a suit, would you really want to work for a person like that?
Hope that helps,
Shawn