It's also worth noting that Philip Greenspun have also pointed out that using a ram disk or throwing lots of cache at a disk-stored database is not the only way to improve performance. ACS for example is based on good data models. The ACS utilizes a great scripting language for beginners.. using tools like AOLserver to help most anyone poke at the data quickly. The ACS also states guidelines for improving perceived performance for users who access these scripts. Things like returning a complete blob of text instead of repeat ns_writes when it's appropriate.. or refraining from using tables when the individual rows comes slowly (because Netscape won't render the arriving rows as they come--waiting until the close table tag arrives--agh!).. or showing as much personalized information as possible from the very first page the user visits. The ACS data model also reflects the fruit of extensive and ongoing SQL tuning. And so on and so forth.. so ram helps, but that's not the end of the story.
The best way to learn all these things is to download OpenACS and read the documentation, datamodels and source to modules that interest you most.