Problems mousing over variable names in iPhone debugger

For future reference, there are several major causes:

• Target-level optimization settings: there should be no optimization
• Target-level strip symbols: symbols should not be stripped
• Target-level level of debugging symbols: default or all symbols should be used
• Per-file compiler flags (get-info on file, choose Debug tab): Make sure there are no optimization per-file settings as there is no way to specify in what configuration (debug or release) they should be used, so they're always used.

I go into more detail here.