After the system update to Lion my iMac (20 ", mid-2007) was already become very slow with 2GB RAM. An upgrade to 4GB RAM should help. Spontaneously I ordered not as of A. recommended in A. Store the upgrade for 200.00 EUR but this RAM kit from Kingston for only EUR 50.00. The exchange was quick and in the "About This Mac" whopping 4GB RAM to me now displayed. The system performance has significantly improved.