Your experience clearly differs from mine. With 1GB and the same workload, I often had to wait several seconds when changing from app to app.
Well I haven't experienced Leopard on anything less than 1 GB, but I didn't imagine it to be that bad on 1 GB. On Tiger, 1GB RAM is more than enough for my needs. But anyway, like I said, DDR2 RAM being so cheap, it makes sense to get 2 GB just in case.