I'm on the exact same model (Mid-2012 15" rMBP, 8 GB Ram, 2.3 GHz Core i7). So far, things are still a bit buggy and rough around the edges IMO, but nothing seems Retina-specific. In my experience so far,
Mail is fairly buggy. Sometimes, Mail won't move messages between folders on the same account, and I've found that the "archive" button will at times delete a different message than the message that is highlighted when I select the archive button.
The Messages app is having trouble distinguishing if an out-going SMS message should be sent as an SMS or an iMessage. When I try to send an SMS to a friend's phone number, at very random times it will send as an iMessage (and then fail to send). Picture messaging is also buggy, frequently saying a picture has not been delivered, but sometimes actually delivering it (iMessage specific, SMS pics work fine).
Continuity has greatly improved on the second developer's preview, although certainly not perfect yet. If the device actually recognizes an open application on another device (happens only 50% of the time) the transition opens very slowly (so it will sometimes take up to 20 seconds to open an email on my Mac that I started composing on my iPhone). Oftentimes, when the out-going message does open on my Mac, it will take an additional 10 seconds to load the message content I've already typed from my iPhone. Lastly, from time to time, a notification on my Mac stating "iPhone is not available for continuity with this Mac" will appear. Sometimes it is immediately followed by a message stating it is available, other times it remains unavailable until I restart both devices. This issue may also be caused by iOS 8 beta 2 on my iPhone 5 too, hard to say for sure.
Last major issue, phone calls from my Mac simply won't work (incoming and outgoing). When I see a phone number in safari and I highlight it choosing the option to "Call '(XXX) XXX-XXXX' using iPhone", the FaceTime application opens and nothing else happens. No phone call is initiated on my iPhone either. When my iPhone received an incoming mobile call, no notification appears on my Mac. Again, this might be an iOS 8 beta 2 bug.
That's all I can think of right now really... decreased battery life maybe. It's an early build still so I fully expect issues, nothing too out of the ordinary.