If you log-in to the PS Vita right now, you will be prompted to download update 3.52. You need to download the update before you can visit the PlayStation Store or play online.
The PlayStation Twitter page says PS Vita update 3.52 is "a minor update designed to improve stability". It doesn't appear as if any other things have been added to this update sadly.
PS Vita update 3.52 is only 127MB. It shouldn't take you too long to download it since it doesn't add much other than the improved stability as mentioned above.
[Source: Attack of the fanboy]