Disadvantages of 32 bit mode
Not inherently.  32 bit mode should run fine as long as all your drivers and binaries include a 32-bit version, which is currently the case unless you specifically downloaded 64-bit versions.  It should even use a little less ram.  

But:


Mountain Lion will be 64-bit only, so I don't expect universal binaries to include 32-bit versions forever.
I have "slimmed" all my binaries to delete the 32-bit version.  If you have ever used such space-saving utilities, the slimmed apps won't work.