For all practical purposes, Second Life is not compatible with MacBook Pros.
Um, not really true.
Second Life reportedly runs fine on the MacBook Pros with the ATI X1600 chipsets.
There were some driver issues that plagued the MacBook Pros with the NVIDIA 8600M GT chipsets and caused hard lockups and terrible frame rates, but these have been addressed by a combination of OS X 10.5.2, the Leopard Graphics Update, and the latest official Second Life viewer. (I'm using one of these of the June 2007 revision and can attest that Second Life runs fine even with all the Windlight effects enabled, albeit slower than in Windows.)
There may be a new issue with the latest revision of the MacBook Pro (the Penryn ones, which also use the NVIDIA 8600M GT); I haven't heard anything official though.