While I don't disagree with you in regards to how PCs are typically used these day, having 1TB+ of RAM could be very useful, and it could pretty easily be made into a virtual disk drive, where the HDD, SSD, or similar is just the "hard" copy, or backup that's loaded from a cold boot, and periodically written to during low computer use, or when being shut down.
The main problem with using RAM in this way is that it's volatile memory, and the data on it is lost during a power failure. Even so, because of it's extremely fast speed compared to other storage devices, it can very much be worth it. That aside, were 1TB+ of real RAM to quickly become readily available, I think it might change how computers are used, and we might not use traditional disk drives anymore, other than as backups, or the like. We would likely need a different power management system in place, and possibly battery power backup for suspended data storage on the RAM.
Personally, I just leave my computer on nearly all the time and do periodic backups of my RAM drive. But I also use it as a Minecraft server, a mainframe of sorts for my Nexus 7 tablet, and crunch for BOINC on it.
Also, features such as SuperFetch make use of "excessive" RAM, working as a smart HDD cache to speed up the computer, in some cases, very significantly, like whole computer virus scans that only take a couple minutes to run that would otherwise maybe take an hour or so.