Say if you want to upload all your documents somewhere what would be the most long term and reliable website?

Since the megaupload incident (legally stored data is being held ransom by law enforcement, they took down the whole service instead of eliminating only those Accounts/files with illegal contents) you can only trust big players.

But even those big players are not feeling responsible for your data, you have to read carefully the terms of use and such (Who may have access, is it encrypted, how often is your stuff backed up etc.). In most cases: If your data is lost somehow, then that's solely your own problem.

Bottom line: You have to "trust" that they don't do stuff with your personal files.

Yes, that goes for pretty much any service in life. That's why banks and corporations in US are too big to fail.
Can you name a couple of "big players" in this area?

The fact is an individual can never match near infinite redundancy these services have.

Google Drive, Microsoft Skydrive, Dropbox. All three provide some free storage. I've used Skydrive as a not-stored-in-my-home archive and will try Drive sometime soon. I keep my docs inside a Truecrypt folder and simply upload the folder (archived) to the cloud. If some three letter agency really wants to use massive amounts of computing power to look at my utility bills, good for them. Skydrive was slow (I remember vaguely 45min to upload 500MB), but I'm not looking to sync stuff back and forth.

I've had a pleasant experience with Dropbox, not much hassle and okay speeds. Most of my friends use Dropbox, one also uses Google to share stuff, as it integrates well with their Android devices. There are also backup services offered by antivirus software companies like F-Secure, which I would assume are somewhat trustworthy and long-lived, but the space offered is rather limited.

I would avoid places like Mediafire or Minus that concentrate on sharing the files, as they may get targeted in anti-piracy action.

It's not tinfoil-hattery to assume your data will be exposed and mined, either by accident/negligence (Sony) or on purpose (Facebook), so encrypt anything that is personal BEFORE sending it out into the wild. The more prevalent cloud services become, the more likely it is someone will want to get their hands on those vast data vaults. With modern processing power and apps like TrueCrypt the encryption happens seamlessly, and you can sleep easy.

US authorities are notorious for snooping, but even a friendly, harmless place like Sweden actively monitors not just offenders, but ALL traffic. "Be vigilant."