According to Scooter Braun, Justin Bieber's manager, and several Justin Bieber fansites that he's been tweeting back and forth with, "Boyfriend" is all but sure to post a sales debut north of 500K copies.
As of approximately 9AM CST on Saturday March 31, Boyfriend had sold over 410,000 copies.
In addition, Scooter tweeted at 1AM CST, on Sunday, April 1, saying that Bieber was "EXTREMELY close" to 500K units, with some fansites suggesting Bieber had already crossed into the 490K range.
If it had sold 410k at 9AM yesterday, and was STILL #1 at that time, albeit not for much longer, then another 90k isn't hard. Fun. is only ahead by 10% on iTunes and the #3 song is below 70%. Its Day 7 and the song is still selling huge & the airplay ain't bad.