Every week I find myself shocked to learn about a new dumb thing that SEOs think will get their site to the first page. Apparently people have been creating custom 404s and linking out from them in an attempt to improve their sites! Or - get this - they've been building links to their 404 pages. What the what?! The thing is - "Google doesn't crawl to see what is on 404 pages, there's no SEO benefit" as written in The SEM Post.
Good Lord, people! Are there folks out there that desperate that they think their 404 pages are the secret to unlocking their salvation? I'm just floored by this idea. Thankful to The SEM Post for covering this issue though. Check out some other links in that article about how 404s (alone) do not cause any kind of penalty. I can't tell you how many times I've talked to a newbie SEO who thought that 404s were the thing holding them back. In reality, 404s are probably more often the symptom than they are the problem!