I use MAMP Pro for local development and after upgrading to Snow Leopard it seemed to slow down when it came to the initial connection to my testing domains. When I upgraded to Lion I also upgraded MAMP Pro and the problem became even worse. So much that it could take upwards of 5-7 second for a fresh WordPress install to load in the browser. After some searching around I found a dead forum post at http://forum.mamp.info/viewtopic.php?f=6&t=14081 where someone suggests using anything but .local for your domain names. Sure enough after firing up MAMP Pro and changing one of my test domains over to .devel from .local everything worked perfectly and MAMP Pro is back to being fast locally like it used to be.
The forum post offers some explanation that since Apple uses .local for Bonjour that due to something new in Lion it has started to cause real issue.