Okay Sunday evening, chilling out, watching some bass vids on YouTube and I come across this.
http://www.youtube.com/watch?v=nywZCDQoNU0&feature=endscreen&NR=1
 Now I am not a Billy Sheehan fan but he has a great reputation of being a superb rock bass player but at 2.20 on the vid he explains that he has bolted a lump of brass at the headstock to add mass! Now what I want to know is that why would you do that! To be frankly honest I think it is a load of bull****. I am sure that Yamaha have spent a lot of time and money in their R & D dept developing there basses only for someone to screw a lump of metal on them.
Can you imagine the nightmare scenario if we Alembic owners did that?
Explanations please..however ludricus.
(Oh yes, his bass sounds really bad too!)

Terry; I think the fatfinger was developed for people playing basses (and guitars) with necks made of a single piece of wood that tended to have dead spots.  The dead spots would tend to reduce sustain.  The effect that the fatfinger had on the neck depended upon where you clamped it on the headstock.
 
Of course another way to address the problem (and in my view a significantly better way) is to build the instrument with a multi-ply neck.  And in my own somewhat biased view, the multi-ply neck looks a lot nicer than the single-ply with clamp attached.

Oh ... and yes; .

It actually works. The Fender style necks and head shapes, even on laminated necks I own, have dead spots. On my basses it is usually around the fifth fret on the G string and somewhat less on the 10th fret of the D string. It has to do with the mass of the head related to the neck. By adding the extra weight you hopefully move the dead spot out of the range of the neck.
 
Keith

Meant to ask, Are you staying cool up there Dave?. Definitely not down here.  
 
Keith

It's 88 here in the living room; a bit cooler downstairs in the kitchen.  And it's a bit cloudy outside right now, so it's cooled to 88 outside as a result; there are distant sounds of thunder, and I'm hoping for some rain.  The current forecast suggests that the next hour or so is the best chance we're going to get for some rain.

What I wouldn't give for 88 right now. According to the thermometer we've finally dropped below 100 with the clouds moving in.  
 
Keith

I've carefully applied a C-clamp to the headstock of more than a few basses when recording.  Sometimes it works really well and other times it's not so noticeable.  The more strings an instrument has, in my experience, the more consistent the tone across the neck and up/down the fingerboard.  I assume the extra tension has a stiffening effect.
 
Only hit 101 degrees here in West-Central Indiana today, and it's dry enough that it's bearable.  We haven't had any rain since mid-May though, and the fire danger is significant.  We need rain.
 
Might be in your neck of the woods next weekend, Dave, as we have a long weekend and will be in search of some cool mountain camping..
 
John

Sorry guys.. I ain't convinced about clamping/screwing metal to your instruments. It's like bolting a cheap 'go faster' body kit to a Ferarri..
I may be lucky but my 83 Squier P bass doesn't have any dead spots at all and it has an Alembic P/J pick up set up.
On another note here in the UK our summer is dead in the water..literally!(rain, rain and more rain)
Maybe I am the exception

That was Freaking Cool Dave!!!! Great Link

John; would love to meet up with you if you're in the area and your schedule allows!
 
Pete; yeah, I've watched it several times; they tear it up.
 
We just had a really good rainstorm (yay!)(it even hailed for a while), and it's cooled off pretty good; so I'm off to the grocery store.

I have a co-worker who a member of the American Guild of Luthiers.  He's also an Electonics Engineer, and holds a number of patents in regard to circuits, etc.  
We had a discussion in regards to the dead spot/fatfinger combo.
Bottom line is, what is being dealt with is a combo of physics/materials.  I have a Peavey Palaedium. 34, (ebony board, w/2 graphite strips running the neck's length), and the whole thing rings like a bell.
My Lakland 55-02, 35, graphite strips in neck, maple board, has the noticable dead spot.  Not as much as my '77 Jazz (the worst of the lot),  but still present.
 
Lee Sklar uses/endorses the Fatfinger and, quite frankly, that's good enough for me.  I don't use one, but if I spent alot of time in the studio, I would consider using one.  But, NEVER on my '77---that thing weighs 12lbs. as it is!  (but what a sound!  lol )

Terry, there is no doubt that changing the weight of the headstock will cause a dead spot to move, or disappear. I have read many anecdotes regarding this problem, which seems fairly common, though not universal, among bolt on, one piece necks. Some have devised crafty ways to hide the additional weight, without attaching a fat finger.
 
I have had a real world example of this phenomenon. I purchased an 87 Japanese Precision bass, that someone had removed the original tuners and put on some very light weight replacements. This bass had a significant dead spot at the 7th fret of the G string. I wanted to bring the bass back to a more original condition, so I installed the Hipshot version of the original open gear clover leaf tuners, which were noticeably heavier. The dead spot disappeared. I can understand your aesthetic opposition, but the science is real, not snake oil.
 
Of the 7 or 8 one piece, bolt-on necks I've owned, only two have had dead spots. The G&L ASAT was pretty minor, and I learned to ignore it. The 87 P bass I mentioned was really bad, and if the new tuners hadn't fixed it I would have replaced the neck, or maybe bolted on a fat finger, who knows..........

I used to play a fender exclusively. I found the best way to cure the flat spot was to buy an alembic and never touch the fender again :-)
 
Graeme

All that talent and such horrible tone.