In the long run the most important thing about your resume is that it can get you fired and/or sued, so you have to be careful to ensure that absolutely everything you say is both true and verifiable through third parties.
The best way to get a job, of course, is through personal contact. In that case your new employer will want to file your resume as a matter of good housekeeping, but there are no real issues there for you to worry about - other than, of course, ensuring that nothing you say in it can be used either against your friends when their business gets sued or to make you the scapegoat if financing or legal issues eventually go against them.
In the most common case, however, your resume has one key job: to get you an interview among uncaring strangers without challenging the ultimate decision makers - and in that context both what you choose to present and how you do that will significantly influence your chances of getting to the next step.
The hidden difficulty in doing that comes from the fact that the resume is likely to be reviewed by many people representing both competing agendas and different skill levels.
In the most typical case resumes are pre-screened on arrival by a computer program or junior assistant with absolutely no embedded knowledge of IT - just some hidden assumptions about format and appearance together with a script on how to check for compliance with some advertised or unadvertised set of expectations.
To survive those, meet the obvious expectations:
The reason for that is simple: only PC bigots really care about this stuff, so using Word sucks up to those who care, while not annoying those who don't - and using the previous release means that most recruitment software will work with it, facilitates access by non Word users, and gives any PC bigots it gets to an opportunity to feel superior, and therefore unthreatened.
The reason is simple and two fold: first, some email responses simply get lost in the shuffle, and, more importantly, the paper copy demonstrates a commitment most of the email responses won't have - and will therefore make you stand out from the crowd.
And, of course there's an exception: for higher level jobs, expect a higher level recruiter: so use a PDF instead of a Word file because it's marginally harder to change and says you're committed to knowledge portability, not captive to one vendor, and at least somewhat aware of the world beyond the PC desktop.
Remember: anybody in the process can say "no" - but only the final decision maker can say yes. So once you get past the first hurdle - the person or program who sorts responses into the "garbage" and "possible" piles - you need to address the recruiter: and whether that person works in a corporate HR role or for a placement agency makes little difference.
He (they're often women, but writing "he or she" everywhere is absurd - except on a resume) will generally have little more than the most romantic and stylised idea of what the job entails and be working from a formal or informal script based on noting keywords and nodding knowledgeably when someone elsewhere in the food chain described what the job requires and what the ideal applicant should be able to do.
In an interview such people can seem competent and often make good judgements about applicants, but they're usually bluffing on the competence and basing their judgements on issues of personality, appearance, literacy, and confidence.
At the resume reading stage, however, they often have handy technology helpers you can use to get the interview. Specifically, they'll often have a resume search engine - or even just a bunch of Word macros- that highlights the key words of interest as they appear in a series of documents (resumes) being reviewed. Because these things do something humans often don't: search the whole document before making a decision on whether a word appears or not, you can use them to put key words aimed at the recruiter into second and subsequent pages while dedicating the first page to real information for the ultimate decision maker.
The first page,therefore, should:
WHy? because a resume that gets you an interview with the recruiter, gets passd to his client - who's only going to skim the first page - and that first page should therefore be aimed at him, not the recruiter.
Unfortunately, when you mention your experience with Red Hat on page one, a recruiter looking for Solaris isn't going to see any relationship to what he's looking for - so what you do is put this information later in the resume and rely on his word search engine to highlight the words he's looking for.
On these pages you summarise each job and role you've had, using as many applicable synonyms and techie terms as you can possibly think of. Solaris is also Unix, if there was an HP-UX box somewhere in the building mention walking past it; if you've used several Linux distributions, mention each one by name - cover the ground, because you can't predict what he's looking for, but you know he won't find what you don't mention.
Don't mis-understand: I'm not telling you to lie or exaggerate: I'm telling you that SuSe experience is directly portable to Red Hat or any other Linux, but a recruiter told to look for someone familiar with Debian will find someone mentioning Debian on their resume while righteously ignored applicants citing expertise with other distributions.
And if you succeed.. the recruiter will call you in for an interview - but that's tomorrow's topic.