I use VMware frequently doing testing with VMware ESX, sometimes with 2-3 sessions at a time. I have 3GB on my MB and any extra memory would definitely help.

I bought my RAM at Thundermatch at LYP which had the cheapest (at that time) 2GB stick of branded memory. Apacer was RM360, Kingston Value RAM were going for around RM420. 1GB sticks are dirt cheap now.

I'm using a pre-Santa Rosa Macbook so it won't register the 4GB RAM even if I put 2x2GB in there, it's an Intel chipset limitation. The performance difference is insignificant if you read through some of the Barefeats and OWC benchmarks, having the extra 1GB makes up for any performance hit.

So, no problems so far, even with memory intensive VMware Fusion sessions.