If you have good timing you'll have already seen it, but if not then be prepared - a Wii U system update awaits. On our system it kicked in automatically when the console was booted up, and it's clear from the download and install time that it's a spit and polish effort, not a major change.
Having checked the Nintendo of America site, the change log for version 3.0.1 U isn't exactly lengthy.
Further improvements to overall system stability and software compatibility
That's a line we've seen plenty of times over the years for DSi, Wii and 3DS updates, and we typically assume that Nintendo's tightening up security and anti-hacking measures. With hackers recently claiming to have cracked the Wii U, it wouldn't be surprising if this update is part of a plan to head off that prospect.
Still, keep your eye out for that improved system stability; if your Wii U doesn't crash today, let's assume the update did its job.