Livid, what industry are you in? What's the position for? Because this greatly affects how formal you should carry yourself. If you're applying for some stuffy government job or a business or marketing type position that requires that you interact with people in a formal matter as part of your job, then you should probably address them formally. If you're applying for an engineering position (particularly within software) or a creative/artistic position you can (and should) be much less formal. Like Steven said, I'd try to address the person if possible. If it's a group, "Dear all" is fine as Koobie mentioned. Really, most people aren't going to care that much as long as it doesn't read "Dear f***face"
(Edit: Rant follows, I hate formal business nonsense)
I'm in software so I'll use that as an example. Of all the big software companies you could work for, the best are the ones that are informal. Microsoft, Google, Apple, Amazon etc. You'd never interview with those guys wearing a suit. Wearing a t-shirt and jeans is completely acceptable. You'd never write a formal business letter to a recruiter. These are pretty smart companies and they recognize that these traditional practices are
garbage and have nothing to do with how well you do your job. All the people I've talked to and interviewed with at these types of companies really just prefer to talk to
people. Address them as individuals like you're having a normal conversation.
And just as an aside, I think dress code can be an oddly telling factor about a lot of companies. I hate dress codes, with a freaking passion. If all I do is sit in an office or cube all day and write code, occasionally meeting with coworkers, there's no need for me to dress up. It does not make me "more productive," that's early 20th century managerial bull****. A lax dress code doesn't necessarily tell you anything good about a company but a strict dress code, at least at a software company, is a sign to run far, far away. If I walked into an office and saw all the developers in shirts, ties or suits I'd immediately think "
this company writes terrible software." If someone told me that I had to wear a shirt and tie to work everyday I'd head for the door.
Bassoon, n. A brazen instrument into which a fool blows out his brains.