You can get it REALLY tight with Zip ties, at least with motherboards with holes, or slotkets.
If you're not getting a really tight, flush fit, then yeah, i agree, but I have had good results in the past with the Ziptie technique. You can get it really tight.
I always use COPPER SPACERS to avoid crushing the delicate CPU die. try 3dcool.com or 3dfxcool.com for copper spacers, usually around the $10 range. worth the insurance to protect your core from possible crackage.