The Market app is missing from the launcher dock. I have verified that the Vending.apk file is in the /system directory and it does show up in the list of applications, but when I open the dock (using the stock launcher), it isn't in the list. The Market widget is also not available in the list of widgets.
I tried removing the application with TiBU and then installing a new one via adb and after it launches it FCs and then actually disappears from the list of applications in the dock.
I tried flashing the 5.1 again, but that didn't make any difference.
I did a wipe when I first loaded 5.0 but I haven't done a wipe when upgrading to 5.01 and then 5.1. The Market app was there in 5.01.