This one may seem obvious, and you have to have access to the necessary file for it to work, but if that's the case your life suddenly becomes much easier... albeit temporarily.

Say you're revising someone else's pre-recorded VO or vocal track - perhaps for a script or part rewrite. Actually, this helps for any time you need to re-do what someone else did and stick to their sound qualities. You have a time crunch and you need to match their EQ or compression settings and would rather avoid just trying to get it close through your own noodling. If you can snag the very small Pro Tools session icon file, do so.

Import it into your session through "Import Session Data" (in PT incarnations 6 and up). Take their (hopefully labeled) VO track, and import the settings. Assuming you own the necessary plug-ins used in the previous session, the plug-ins and their settings will show right up. Drag them into your track and you're good to go. Even if you don't own exactly what they do, you'll get an immediate clue as to how much they colored or slammed their track.

Obvious discrepancies can happen if different mics are used, or the recording environment is different, etc., but it gives you an immediate solution when clients are breathing down your neck.