Depending on the industry you work in, there are arguments for and against as to whether cover letters should still complement a CV application in a frantically competitive market.
If you're applying directly to a potential employer, then a succinct and easily digestible cover letter/email should still be encouraged. It really is your chance to explain why you are applying for both the company and the role in question, so it needs to be tailored appropriately.
If you are applying for roles via an agency, then it becomes relatively less important to write tailored application letters for every position - it should be down to your recruiter to ensure they 'sell' you to their specific clients effectively.
If you want to stand out from the crowd, then tailoring your CV as much as your cover letter should help too.
Don't forget to proof read either - if you can't be bothered to check your spelling and grammar, then don't be surprised if you get overlooked!
It’s an overstated but vital point that employers don’t have a lot of time to look at job applications, so cover letters should always be kept short and succinct.