To name a few:

Often, the PC would hang, the screen would go blank and the system tray would alert me that the display driver had to be reset. This has happened on multiple PCs around the IT department, so isn't singled to mine.

Using sp_helptext and copying into a new query window adds a carriage return between each line - rendering it fairly useless unless you use the 'results to text' option.

I have a share on the network where I save SQL scripts and other utilities. In 2008 I open this folder directly from SSMS, and each time I click open file it remembers the last location I opened - handy in a rush. 2012 does not, and often opens at the C:\Windows\System32 location??

This one was very weird - Opening a folder sometimes caused the open file dialog to disappear. I then had to maximize another window, normally outlook, to get the file dialog to reappear.

I sometimes received a 'System.OutOfMemory Exception' when viewing some execution plans. These plans render in 2008.

That was my dealings with SSMS 2012. I got rid and went back to 2208 after that...