a) Ability to group circles. Ie: Make a circle that contains circles!
b) instead of single circle stream or Stream (all) - add ability to pick multiple circles to view in the stream. There are some people whom you follow (like Jason Hiner) who post so much stuff that if you put them into a circle and view stream - they drown out everything else! (Sorry Jason

)
c) GTalk is integrated - right there on the left side under Chat

d) Add location is too restrictive - it often puts you close, but not at where you are. Need ability to tweak the location, like manually adding the actual address - and having the system learn from that.
e) related to above - integrate Latitude correctly - a bit screwed up now!
f) You can already sign up with ANY EMAIL ACCOUNT - just need a google profile!
g) Ability to pick a SINGLE photo from an ALBUM and share that! Currently can only share selected photos from your instant upload - not from ALBUMs
h) And when people get the temptation to start building games for G+, PLEASE PLEASE PLEASE give us the ability to block classes of applications from posting to us - ever!
i) related to above - make seperate NOTIFICATION area for such 'application' type alerts.
I could go on a bit, but these are my top points!
Cheers