Many, when debating the likely outcome of a particularly recruit's career, will reference how one of the scouting services have ranked them, while others will cite one of a handful of lower ranked recruits who met with success (David Harris, Braylon Edwards, Mike Hart come to mind). In the interest of quantifying whether recruit rankings can be, at all, predictive, here are the raw numbers on whether a recruit has panned out, sorted by star ranking.
First, I would like to note that all rankings are from Rivals, and that kickers and punters are not included (no kicker or punter is ever ranked higher than 3 stars) and does not include the 2007 or 2008 classes due to it being too early to tell. Finally, I am defining "success" as being the principle starter for at least one season.
In the 2002-2006 classes, we recruited 6 5* players, 5 of whom became starters (Grady has, and likely will, not).
We recruited 51 4-star players - 26 of whom became starters (about 51%).
We recruited 40 3-star or lower players - 9 of whom became starters (22.5%).
So, four star players are roughly twice as likely to grow to be a starter than three-star players. Further, the "drop out" rate of 3-stars is significantly higher - a larger number of 4-stars who did not become starters stayed with the team and provided depth. The mumber of 3-stars who simply quit football is much, much higher.
Lest people think I'm on the side of "Rodriguez shouldn't offer three-stars", that point of view is, in a word, dumb. Three-stars DO succeed, no team can have a class of 5 and 4 stars unless you're USC, and we need to have them. Further, ones offered this early at least FEEL like they may be better, because Rodriguez has more confidence in them. That said, recruits of all ratings miss, and three stars miss considerably more often than higher-ranked players - it is for likely we never hear of them again than it is that they become Bradent Englemon, musch less Mike Hart.