As above. Is it needed where new gaskets are used with good mating surfaces. i.e. oil pumps. water pumps, thermostat housings.
Advice given so far is has been conflicting.
Advice from those that have experienced and not experienced leaks, most welcome.
If the vote goes for a jointing compound,which one?

I have designed gaskets for air compressors in my past Engineering roles.

I NEVER advised using a jointing compound - bit of a bodge in my opinion and in the opinion of the gasket material manufacturers.

Edit to add; a well designed joint shouldn't need jointing compound.

[Edited on 24/2/09 by JAG]

If the gasket is new and the mating surfaces in good condition then shouldn't be needed.

Stu

If you need a good sealant try Wellseal.

Good for everything apart from thermostats etc.

Leaves no strings if over applied.

I don't use it on new gaskets with clean surfaces.

but it may be useful for example on a sump to keep the gasket in place before it is bolted.

I have found lumps of gasket in coooling systems before, !!!

I've used it to seal the throttle pot onto my D-spindle adaptor for the EFi. Not sure how I'd feel about using it on the oily side of things...

I use Blue Hylomar on less than perfect gasket faces. It's non-hardening so the gasket can be removed in the future (albeit with some effort), unlike the red stuff that appears to turn into some kind of concrete.

When replacing the two plastic water outlets on my Golf cylinder head I cleaned up the head faces and it left the aluminium so pitted that I couldn't get a seal with the supplied rubber ring gasket.

I wadged Hermetite Orange there and it's lasted 30+ thousand miles so far.

Thanks to Stu (and Fozzie) for that suggestion!

Cheers,
James