It's doing well. Much better than 3DS or Vita launches, but no where near the hysteria of the Wii launch in 2006.
That was insane trying to find one, I remember some older housewife type in front of me had a melt down when the store started turning people away, lol.
If you really want one and/or are willing to settle for the Basic pack, you can probably still find a Wii U today with a little looking around at retail.