If you could change "one" thing about Facebook, Twitter, YouTube and LinkedIn, What would they be?

Facebook :
1- Make Dislike Button, I see a lot of annoying posts.
I want to dislike them
2- remove all crazy game requests Twitter: - The limitation is killing .
I'll make it 240 chr at least.
Youtube: - Remove Crazy and annoying ads LinkedIn: - enhance the endorsed flow , it's crazy you get endorsed from people they don't even know you.

Facebook: - Less suggested posts.
- Less game invites.
- A clear privacy system so users know what they're opting in/out of.
- Less intrusive information grabbing, forcing you to change or add things to your profile like where you went to school etc.
- Less advertising.
- Removal of poke system.
- A way to stop companies and apps asking if they can post to facebook on your behalf when you sign up or opt in to things.
Twitter - I'm quite happy with the140 characters, however for times when more characters are needed a tweetlonger system should be inbuilt rather then having to go to the3rd party app.
- Scheduled tweeting would be incredibly useful for those of us who work within social media.
Again I know there is an app that allows for it but I'd rather have it inbuilt.
- Not using links or photos as characters but rather leave the140 in tact for comment.
YouTube - To separate youtube and the google mail accounts automatically and not have youtube force upon you a merge.
- Less annoying adverts.
- Parental control settings.
LinkedIn - A better contact system.
- A better way to add people only if you REALLY know them.
Now you can bypass this by clicking on the friend option when asking to add someone.
- A way to block certain people from seeing your information.
You may want them on your list (for example current bosses) but if you're job hunting you may not want them to know of this - or you may not want some people to know a lot about your work, etc.
- Less ads.
- A way to separate feed - one for people looking for work - one for people who have endorsed or changed information on their page, so that you can pinpoint exactly what you're looking for without having to go through all the posts.

Facebook: Not allow someone to see comments one of their friends posted to someone else's page if he or she isn't friends with that person as well. 
I'm also not happy about the business page situation with FB cutting back on how often the page is shown on the feed unless it's paid for! Twitter: The characters limit.
"That 140 chr limit makes every1 spks like a teenager!" Youtube:  The ads before the video which can't even be skipped! LinkedIn: well, I think the endorsements section needs a lot of improvements! I mean i'm being endorsed on skills that I didn't list in my profile!

well, facebook: the adds on the right side, & the endless useless games twitter: not a fan of twitter :P Youtube: the ads that are associated with every video Linkedin: i think it's fine as it is :)

I would grant users more power over eliminating "noise".
This will not only help me as a marketer to target a very spot-on target, but will also declutter space thus allowing the target to actually see the content and if everything goes to plan, engage with it and convert.

Facebook: Rework the Privacy settings - Even with all the options available for limiting your profile, it's still possible to view tags on photos, statuses, etc.
if you have mutual friends with the other person.
Also, anyone who signs up for a new Facebook account would easily get lost in the privacy settings, Account settings, etc.
They should come up with an easier way of viewing these options in an easier way; Twitter: If there are links attached to a tweet, those characters used shouldn't count since the limit is already too less; Youtube: The ads that are being played which have a 5 second delay (I think) before you can skip them - seems forced on to users; LinkedIn: The number of users with fake credentials (eg.
HR companies) who connect with users and then add their connections for their own benefit.
Most of the time, they aren't even HR professionals!

Definitely I will add the Dislike Button which will reduce the number of content created and posts dramatically

For me, being an internet marketing Expert & to some extent specialization in product development, I believe that I will implement one social media integrated row toolbar in all above mentioned social media where a user can easily integrated all his/her account on the same page.
Like if he is using a Facebook, on the same page, he can successfully connected and integrated his twitter, LinkedIn & YouTube account through Web Development JQuery page scroll Based social media accounts integrated toolbar.
Have a Nice Day.
Syed Waqas Saghir Internet Marketing Expert, SEO Consultant, Social Media Evangelist.
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- In Facebook will add dislike button.
- In Twitter would add Insight Just like FB for reporting , Number of retweets per moth, how many people reach through a # tag etc , so there will be no need to use third party tool for reporting:) - In YouTube the ads they are showing inside the Video.
It's useless because i think while watching an interesting video who will click on ad? - In LinkedIn would add Business Marketing feature ( Banner ads) in their default ads system.So there will be only one platform for text , video and banner ads.
I would also add Arabic language in their text ad.

Twitter: - Ability to tweet to certain lists only Facebook: - Ability to search content (e.g : My post about funny cat video)

The content, I think it is not beneficial to contain unnecessary videos or posts on the social media platforms, because they have destructive effects on some people. So, I suggest they have to be monitored and filtered from such these things.