I'm working on something big (and, I expect, both redundant and slightly negative), so I'm not going to write too much today, but I did find two articles worth posting.
First, via Access Vikings, NFL.com has an article that talks about teams playing "Big" Nickel and how the Vikings gave themselves that option by drafting Tyrell Johnson. Basically, "Big" Nickel is a package where you use a third safety as the nickel back rather than a third corner and it's used for two reasons, the first, of course, being that your third safety is better in coverage than your third corner. It wouldn't surprise me if this was true for the Vikings next year, especially considering that Tyrell Johnson is fast for a safety and has great closing speed. It's also used against offenses that feature quality tight ends, as the bigger safety is usually able to handle tight ends better than the smaller corner. Even though the Vikings will have seven games against teams with tight ends that had over 500 yards receiving last year (GB, HOU, CHI, IND, NYG), I'm not sure that's as big a deal for the Purple, as Marcus McCauley is the same height and only a few pounds lighter than Tyrell Johnson.
Secondly, via Daily Norseman, the Chicago Tribune thinks that the Vikings signed the best class of rookie free agents. Don't underestimate the importance of rookie free agents either, as this article from last year's playoffs points out, they can turn into valuable contributers on playoff and Super Bowl winning teams.