A blazer would be underdressed in my field.
Solid cover top with short sleeves, long loose-fitting jeans with kneepads, and(most important!) no lipstick.
Anything corporate, suit always.
What are the people who are interviewing you wearing? That+1 in formality should be a good guide.
As a rule of thumb, a blazer is a good idea if you’re in any kind of corporate position where you’ll be in direct contact with customers (and by customers, I mean it in the corporate sense, where a “customer” could also be a different department). Different rules apply for strictly behind-the-scenes jobs like IT code monkeys, but those departments tend to march to a different drum in more ways than one
In my position, since we’re pretty much behind the scenes, our interviews are usually done in dressy business casual (shirt and tie for men, professional-looking top and skirt or dress with pumps for women). A blazer or suit wouldn’t hurt, but it might look like you’re trying a little too hard.
I do know of a few fields where a blazer will actually hurt your chances of getting a job. Most of my friends in the animation industry wear t-shirts and jeans to work, from the lowliest juniors all the way up to the company owners. Showing up for an interview in a suit is a major no-no in that field… their version of “dressing up” is basic business casual attire - slacks, nice shirt/sweater, no sneakers. Same goes for what I’ve seen in web design, dot.coms, and most graphic design firms.
OTOH, a sports coat that fits is a lot better than an Armani three piece that’s three sizes too big.
At least in the corporate/semi-corporate world (this includes federal/state/contracting), somewhere around 80% of rejections are due to appearance rather than unsuccessful interviewing. Yes, you need to be good at interviewing too, but it doesn’t matter how good you are if they’ve written you off due to your appearance as soon as you walk in.
One tier better than the position you’re interviewing for is sound advice. For the kind of work I do (network security/IT), even a blazer is underdressed, despite common stereotypes for the IT field. Dark blue or gray suit (never black for males), single-breasted, appropriately tailored. Giving them any reason at all to write you off is job hunt suicide, especially in today’s economy.
ETA: To piggyback on Mahna Mahna’s experiences – if your job doesn’t involve artistic creativity, then don’t be creative.
Maybe not the most appropriate, but that outfit would get you noticed.