When using gdb in Snow Leopard, they system asked me to

Type the name and password of a user in the 'Developer Tools'
group to allow Developer Tools Access to make changes

Huh? I don't want to "make changes", I just want to debug a process. Turns out that monitoring/inspecting a process has been changed in Tiger and again in Leopard so that only members of the 'Developer Tools' group are allowed to debug. (Wow, I have never used gdb on Darwin before?). The right thing to do here is:

sudo dscl . append /Groups/_developer GroupMembership username

...and get on with our actual debugging.