I recently upgraded my MacBook Pro and Mac Pro to OS X Lion, and I've only come across two minor issues.

1. On the Mac Pro I have a really skittish Magic TrackPad … regardless of the settings I apply in system preferences, the cursor is very jumpy and moves too far for the amount of swiping I am doing. I am hoping that Apple comes up with an update to fix this soon… I've tried out BetterTouchTool and, while it gives me more granular control over things like tracking speed, it hasn't done much to alleviate this specific issue.
2. On the MacBook Pro I also added a second SSD drive (the original that shipped with the laptop is running thin, so I grabbed a data doubler from OWC to replace my SuperDrive, which I never use).

   Not sure if it was the Lion upgrade or the addition of the SSD that caused the issue, but I suddenly couldn't run my Boot Camp partition as a virtual machine under VMWare Fusion. When I tried to start it up, I would get this error:

   Cannot open the disk '/Users/AaronBertrand/Library/Application Support/VMware Fusion/Virtual Machines/Boot Camp/Boot Camp.vmwarevm/Boot Camp.vmdk' or one of the snapshot disks it depends on.

   Reason: The partition table on the physical disk has changed since the disk was created. Remove the physical disk from the virtual machine, then add it again.

   I verified that I could boot to the Windows partition on bare metal, and that the virtual machine was intact and running as expected. It also took me a few minutes to find the vmdk file and verify its location, since all Library paths are hidden by default in Lion. To unhide them, open a Terminal window and run:

   chflags nohidden ~/Library/

   So I booted back into OS X Lion and followed these steps:

   • Shut down all VMs
   • In the Virtual Machine Library, right-clicked the Boot Camp VM and selected Delete
     (Don't panic: this doesn't delete the VM, just VMWare's pointers/config files)
   • When asked whether to keep files or move to trash, I kept them (just in case)
   • Clicked on the "Home" option in Virtual Machine Library
   • Clicked on the "Run Windows from your Boot Camp partition" option
      

   Now, when you start up your VM for the first time, VMWare will have to re-initialize the VM, so it will take a few minutes. I suspect this just changes a bunch of bits to the same bits, since the VM should already be optimized to run under Fusion (you'll notice it doesn't go through the VMWare Tools install like it does when you first create a VM or initialize a Boot Camp partition for VMWare).

   You might also find performance a bit sluggish once you're up and running again – this is because VMWare set the CPU and RAM back to their defaults (1 core, 1GB). You will also notice that if you had set a custom CD/DVD drive prior to the OS X Lion upgrade, this is back to the default as well – and you may have to update other custom settings such as shared folders, sound, what have you. Shut down the VM, adjust the settings, and then you should be all set.

   Hope this is useful to some of my fellow Mac converts.