I think it's a potential problem in 4E, but I also think it's a big issue in 3.5, so it doesn't bother me much in 4E. In 3.5, I have a "training" rule (for lack of a better word). Basically, upon gaining a level, a PC needs a month of downtime to absorb the knowledge and be ready to continue his or her "adventuring education." Gaining two levels requires four months. If you haven't had your downtime, you just stop gaining XP at the highest point before gaining the third level, until you take the four months.
It works pretty well in practice, especially because as the PCs end up with disparate amounts of XP, there ends up being extra downtime, because one PC or another may need it, as others may not.
It works well with my DMing style, because I tend to have things simmering in the background of the campaign for months and years ... I'm not a big fan of "you learn today about a plot by the mightiest wizard known to man ... and you have a month to stop it." It's more like, "Huh. That's some weird news out of Xen'drik." Three months later: "Did you hear that giants are massing in numbers within a week's march of Stormreach?" Six months later: "Um, guys, remember that ancient warforged we accidentally activated in those Xen'drik ruins? Looks like he's leading the giants in an assault on Stormreach. We might wanna get down there and stop it."
As much as I dislike the Meek to Mighty phenomenon in general, I really do think it's something for the DM to fix, if he wants to. If he and the players are okay with "plug another quarter in" leveling, cool. If not, the DM only has slightly less power to rein it in in 4E as he had in 3.5, at worst.
I'm sure somebody has mentioned this, but rumor is 4E will have built-in rules for customizing the rate of advancement via XP gained (or XP needed, which amounts to the same thing). If 4E really has done what they say in terms of divorcing magic items from character power, that should be enough right there to give the DM all the power he needs. And the nice thing is, he can vary the speed from tier-to-tier, or even level-to-level.