Since I was the one who got on the soap-box, I'll offer some 
suggestions I've found useful in tracing various vacuum leaks.

1.  Stick a hose in your ear.  Really.  By placing a section of 
heater hose or nearly anything, including a tube from a roll of paper 
towels, against your ear it makes your hearing in that one ear very directional..  
With the unhosed ear plugged (picture me with one hand over one ear, 
a section of heater hose sticking out the other :) sweep across the 
suspect areas until the hiss is loudest then start homing in.  Do 
this in the parking lot of K-Mart and watch the looks you get.

2.  Put a few psi air pressure into the vacuum hose system.  I've 
discussed this one before but essentially hook up a regulated air 
hose dialed down to a few psi, into your vacuum system and listen for 
leaks and use that squirt bottle of soap water to spray hoses, parts, 
etc.  Use caution with this method if you have a vehicle with vacuum 
servo doors in the heating/cooling system as it may inflate the 
bellows designed for a negative pressure, not a positive one.  The 
brake booster often has a check valve in-line so this may not reveal 
a leak in that device.

3.  Systematically, remove the vacuum hose connection from devices 
and plug the end of the hose to remove that device from the vacuum 
circuit. Golf tees work nice for plugging vacuum lines.

4.  Use a vacuum gauge.  This ends up being your 'test meter' and 
have a nice assortment of "T" fittings, hose pieces, and other 
adapters.  This is one of those 'tools' you accumulate thru the years 
and it keeps getting better as you fill out your fittings box.

5.  I don't like the flammable liquids/gases method.  Some people 
spray carb cleaner, use propane, or even starting fluid (ether) to 
spray around while the engine is running to notice an RPM difference. 
 You're on your own with this one.  I've seen too many bad 
experiences with ether, benzene and other organic solvents in the 
chem lab to go spraying them around a hot engine.  (Got a great story 
re: benzene, sink traps, a row of 5 chem sinks, and an open flame...)

-dan