Yup, I agree with warlord2, that stuff is pretty sticky stinky. I read an aritcle on overclockers.com about a year or two ago about that. I don't know if he used "low expanding" foam, but he used foam. And sure enough, it easily lifted the heatsink from processor.
If you do use it, make sure you apply it on the outside and don't let inbetween anyting. Make sure the foam can expand freely "outward". I.e. dont let any foam rest between socket and a component, it will easily push a cap over and may damage it. Also some of theese foams contains a rather strong solvent. My pal got a small spill of foam on his plastic carpeted floor, it melted the floor and sortof joined it.
Also if you use it, maybe you should "paint" the surfaces with grease before applying foam.