Next week's show will be a regular one. I don't think she will be hosting the year end countdown, which will presumably be the following week. No year end AT40 or CT40 has ever been guest hosted.
This will be the second time Katy Perry has hosted AT40; the first time, in August 2009, she got to announce her own hit at #1, which no other AT40 guest host has done thus far (Taylor Swift came close last year, guest hosting on a week she was at #2.) Katy won't repeat that feat this time, but will get to play at least two of her own hits, and possibly others (last week Britney Spears guest hosted and played four of her own songs as extras, in addition to a currently charting hit.)
This would actually be the third time in the Seacrest Era where this has happened.
First: 8/14 and 21/2004, with Hilary & Haylie Duff the first week and Kelly Clarkson the second. Kelly Clarkson's week also marked the sudden appearance of Avril Lavigne's "My Happy Ending" into the countdown, if you know and remember the infamy behind that.
Second: 1/3 and 10/2009, with Brody Jenner (!) the first week and Giuliana Rancic (who I think he was working with on E! network at the time) the second.
It's also worth noting that there was a five-week period in 2011 where he alternated between guest hosts.
July 16: Neil Patrick Harris July 23: Back to host July 30: Joe Jonas August 6: Back to host again August 13: Glee's Kevin McHale and Amber Riley
I...think, at least one of those weeks saw the guest host happen without advance notice.
Yes, I thought she did a nice job as well. And the AT40 staff played for her a clip of Casey introducing the week that "If You Had My Love" debuted and she talked about that a little bit.
J.Lo remembers that her mother used to do what a lot of us on here did: listening to Casey counting down the top 40 every week, and writing it down in a notebook. As she noted, this was before you could look up the charts online, and they didn't know where you could find this Billboard magazine. (Incidentally, the Casey clip was from the May 22, 1999 AT40).
I thought this was one of the better guest hosted AT40s; her intros to the songs and other talk segments, including answers to fans' questions, seemed more informative than usual from guests. I also liked the announcer's segments, listing Lopez's many talents/duties (singer, dancer, actress, businesswoman, etc.) and saying "that's more jobs than Ryan Seacrest!" or somesuch. (These good-natured digs at Seacrest are a staple of guest-hosted AT40s, down to the alleged reasons for his absence.)