Hi there! First of all, sorry about my english! I use my MBP connected to a DELL U2713H 27 inch display (2560 x 1440 through display port), it´s new (I started using it just 3 days ago). The problem is that te mouse cursor jumps, it suddenly apears elsewhere on the screen. I have used the MBP with a Samsung 22 inch display (1920 x 1080) for years and no problem at all, the mouse was perfect. I always use CORDED mouse, actually a Logitech G400, but I tried with my old Microsoft Optical mouse 1.1 too and is the same problem. If I disconnected the display and use the MBP screen, it works great with booth mouses. I design with the mac, so this problem is more frequent when working (large files, multiple programs open). Maybe the video card is not strong enough? or the RAM? My MBP details: 13-inch, Early 2011 Intel i5 2.3 8 GB 1333 mhz DDR3 Intel HD Graphics 3000 512 MB Software Mac OS X Lion 10.7.5 (11G63) Mouse: Logitech G400 CORDED! Keyboard: apple bluetooth. I work as a designer, so the mac is really clean (just a few software installed). No games, no unnecessary soft. Thanks a lot!