I am in the process of upgrading the RAM on my 11/07 iMac and 4/08 Macbook to 4GB and as a result am winding up with four extra 1GB modules. I was thinking of giving the extras to my siblings so that they can upgrade each of their families' Macbooks, which total 4 in all. I have a feeling that their laptops each came with 2 modules of memory totalling 1GB rather than a single 1GB module. So my question is, if they were to replace one of the modules with a 1GB module (thus winding up with 1.5 GB in all), is the fact that the RAM will be mismatched present a problem - or otherwise make it undesirable to replace what's there? Is it worth making the change. Am trying to treat everyone's Macbook the same way! Thanks.