I'm not in a hardcore guild, but I do see the value in combat logs. I even upload some for our guild runs a couple days per week even though I'm not required to do so.
It's easy, too.
1) Get a WoL account for your guild.
2) /combatlog (in-game, to start recording)
3) /combatlog (to stop recording)
4) Start the WoL client from the link on their site.
5) Click on the big button that says "open log file" and then follow the prompts.
An applicant doesn't even have to analyze the combat log. Just upload and call it a day. Let the guild to whom you are applying analyze the data.
I don't really know how to use the expression editor very well, but at a basic level one can quickly see whether someone is using cooldowns properly, how much avoidable damage they're taking, etc.
We usually have a trial period for new folks to see how well they mesh with other guild members and to see how well they do in an actual raid. Many of us have been gaming together for 6-7 years, so there's something to be said for personal interaction. Obviously, hardcore guilds may have different criteria. My $0.02.