Pidgin: Because you just had to lock all the relevant threads...
Shared libraries must NOT be packed with UPX. Packed libraries can only be used statically, which means that two separate instances of the same library will need to be loaded into RAM, basically defeating the purpose of sharing. Read the UPX docs. This obviously applies to all libraries, but the thread is in the Gaim Portable forum because the plan is to have the GTK+ libraries shared between Gaim and The GIMP (and whatever GTK+-using apps that may become part of all this).