When it comes to hdd space, nope--I can't even fill up my 80GB or 74GB drives. You guys must be downloading lots of illegal stuff to be doing that
My desktop has a 300 GB and a 120 GB drive, and I'm always low on space. Really, it's easy to fill up space even without illegal stuff. Modern games tend to come on 3-5 CDs or one installation DVD. They can take anywhere from 1-5 GB to install. DVD rips take up crazy space too, anywhere from 700 MB to several GB depending on length and quality (I mean rips you make yourself of movies you own). Also, you'll want to have space free for defragmenting. Furthermore, did anybody notice how the read and write speeds of the hard drives decreased as more space was taken up? If I understand correctly, to maximize I/O performance, hard drives write on the outside first, working their way to the inside, because the linear velocity is greater on the outter rim than the inner one. The more free space you have, the less you have to resort to that lower-performance region of the hard drive.
Then you have to consider the actual capacity of the drive being less than you bought due to the file system and the 1 GB = 1 billion bytes issue. A "750 GB" drive is really only 699 GB of space, less after the file system and operating system are installed. Add in various programs, add-ons, and space for temp caches, and you might be down to 675 GB of space. Throw in some more space for the recycling bin's temp space and System Restore points (which on my machine take up 1-10 GB of space, and I regularly remove them to save space) and you might be at 650 GB of space.
Now, take that 650 GB of space and start loading games up on it. This doesn't apply to non-gamers, but if you are a gamer, you've probably been collecting games for a number of years, and with games taking anywhere from a couple hundred MB (back in the early 2000's) to a couple GB (today) to install, a game collection might take up 50 or 100 GB. Save files can also take up space, with some games the save files are 10-20 MB each. Throw in a dozen of those per game and you've tacked on several more GB of content. That's how it always is, several GB here and there, a new program, a new temp cache, and it all adds up. If you're a photo buff and every picture is several MB, then a single vacation might end up being a GB of photos. If you like to record video, it adds up crazy fast. If you're an audio buff and enjoy uncompressed audio from your CDs, or you're a movie person and want the quality of a DVD but the access speed and resolution of a PC, space continues to be sucked away by the gigabyte.
Let's say that a game collection, large photo collection, music collection, and movie collection add up to take several hundred GB, which is not unreasonable (my computer being the prime example). Your drive is over half filled, by which point your performance has started to degrade. Putting in more will aggrevate the problem.
If you're the type who records TV shows or downloads unliscensed, fan-subtitled anime, a single show that airs once a week at pretty good quality can take up 170 MB per episode, or about 4.5 GB per 26-week season. And if you buy into the HD-revolution, it can be double that size. A 1280x720 anime episode (lots of still frames, little motion at once, and using the H.264 codec to save space) can take 300-400 MB of space, for a SINGLE episode.
Thus, a mighty 750 GB drive is slowly filled (or quickly, if you already have the content available) with video, music, photos, games, temp caches, and the like.
Now, this isn't to say everyone NEEDS that space. Sure, you can set the recycling bin to immediately delete anything you put there, you can give your 'net programs a whopping 5 MB of cache space, you can purge your computer of video files and keep your MP3 collection at a modest several GB. You can get along with 80 GB of space (my laptop has 40, or 32 after the damn IBM restore partition) if you're thrifty or not a media enthusiast. But as long as drive prices continue to drop, why wouldn't you want the extra space? It keeps your performance from tapering off and if nothing else, makes you feel good when you see that you have 90% space free.