I have recently installed Parallels with the current Leopard suggested build 5582.0 running Windows XP Pro on a MacBook. If I started other Macintosh applications first and then started Parallels the whole system, both Mac and PC sides would slow with an essentially constant "spinning beach ball". If I start Parallel first; and then start other applications on the Mac side; everything runs amazing well. Occasionally I have to double click icons to switch from one application to another but all applications run etc. Just providing this observation.