I have been dealing with this very same issue for over two weeks now. If i manage to get logged in Secondlife works a couple of hours but the next day its the same thing. However I only have this issue on one account, my second account logs in perfectly with zero issues.
I am using the official secondlife viewer, have done a complete clean install and still crash instantly when clothing is downloading.
I opened a few tickets and have yet to receive a solution from LL. If I come across anything that works I will share.
My System info:
Second Life 3.2.5 (247236) Jan 5 2012 12:08:13 (Second Life Release)
Release Notes
CPU: Intel® Core i7-2720QM CPU @ 2.20GHz (2200 MHz)
Memory: 4096 MB
OS Version: Mac OS X 10.6.8 Darwin 10.8.0 Darwin Kernel Version 10.8.0: Tue Jun 7 16:32:41 PDT 2011; root:xnu-1504.15.3~1/RELEASE_X86_64 x86_64
Graphics Card Vendor: ATI Technologies Inc.
Graphics Card: ATI Radeon HD 6750M OpenGL Engine
OpenGL Version: 2.1 ATI-1.6.36
libcurl Version: libcurl/7.21.1 OpenSSL/0.9.8q zlib/1.2.5 c-ares/1.7.1
J2C Decoder Version: KDU v6.4.1
Audio Driver Version: FMOD version 3.750000
Qt Webkit Version: 4.7.1 (version number hard-coded)
Voice Server Version: Not Connected
Built with GCC version 40001