Yes - happens all the time to me since the addition of the Google Play store. I suspect that it is down to the Nook homescreen having to deal with both Nook Apps and Google Apps.
To be honest for me it is a small price to pay to get such a jump in functionality thanks to the addition of Google Play store.
I guess you could download a different launcher from the playstore which may avoid the lag for you.
I get the same message. I think there was such a rush to get the Play Store and Google apps integrated into the Nook HD system that they didn't take the time to go back and tune the system to eliminate any hang-ups that might occur. I also often get a message about "Library is synching" which occurs multiple time within seconds of each other. How often does it need to synch? Also I get messages about apps not responding and do I want to close or wait. It had been performing reasonably well until I downloaded a movie from the B&N Store. I removed the movie but the slow performance persisted. I removed all nonessential apps and turned off synching fir most Google apps. The helped some but performance is still not what it was before I downloaded the movie. I installed Watchdog Lite to see if I can identify the culprit. Hipefully B&N will do some tuning and fix the performance problems in the next update.