The first semi-official figure is out and the PS Vita sold 321,000 units in Japan in its first weekend. There is no breakdown between WiFi and 3G models, but if that rate continues, it will easily hit the million mark by Christmas. Most retailers said they still had the PS Vita in stock, but many had sold out of memory cards which might delay some sales.
That figure is roughly double what the PSP sold in its opening weekend, and just behind the 3DS. These figures will be discussed in an inane fashion by a bunch of people claiming the PSV is either doomed, or totally dead already. Ignore them and we'll see how it is doing in six months after its global launch. Sony will be delighted on the sales of memory cards as that's the only thing it is making a profit on right now.
See Vita launch coverage here.