This is already making the rounds, but I figured I'd add my voice to the chorus, to maximize the likelihood that people find the information that they need.
If you're an ORACLENERD and a relatively early adopter of new versions of Mac OS X, you might notice that the 64-bit version of the OS X Instant Client does not work under OS X Lion. Attempts to use the 64-bit sqlplus binary and libraries result in a segmentation fault. Boo. The only known solutions for command-line sqlplus from Lion at the this point seem to be use the 32-bit client, or stay on Snow Leopard. We're still in the early days of general availability for Lion, so perhaps another solution will surface.
I suspect that this doesn't mean good things for the full-blown database install, but I haven't checked that out yet (and I don't know when/if I will; my native OS X install of 10g had been gathering dust for quite a while, and did not make the move to my new MBP).