I don't look at resumes that don't include a letter of introduction. Here's a few reasons why:
•Starting with "Hello" is the way human relationship begins.
•Most jobs require some sort of communication. That starts with an introduction.
•Resumes are created in advance. Conversly, cover letters SHOULD be customized to match the position and the company hiring. If an applicant doesn't think our position is worth that much effort, then I know they're not very interested, and it probably won't work out.
•I hire based on desire first. The cover letter tells me how strong that desire is.
But the primary goal of the cover letter is to accomplish ONE job - To inspire the employer to actually LOOK at the resume. The cover letter, if composed carefully can capture attention and differentiate from all other applicants.
Recruiters who say that cover letters are largely ineffective are correct - because the majority of cover letters fail miserably at accomplishing the core objective.
In other words, not all introductions are created equal so it's illogical to group them all together and say they do or don't "work".
A properly drafted cover letter will get the resume opened EVERY TIME. Now if your resume sucks, that's another matter entirely.