After my hard disk replacement in April 2012 the same thing happened to me. I bought a corded Apple mouse and keyboard, but missed the functionality of my trackpad.
I received an email 2 days ago from Apple regarding the Seagate replacement program. iMac 1TB Seagate Hard Drive Replacement Program
I suspected an antenna issue, so when I took the iMac 27 to the Genius bar appointment I told them of my experience with extreme limited range and connectivity for them to look for antenna or bluetooth card seating problems. I wish I had had your post from June to show them.
The replacement drive that I paid for in April 2012 was becoming unreliable just as the initial Seagate drive when I purchased in June 2010.
But the letter authorizing only arrived two days ago, fortunately just during 2 days of HD problems. SMART testing passes the HD but shows Seek Errors and Temperature problems with the drive.
I hope to hear from Apple soon and have a perfectly functioning iMac again.