Hi,

could you please try to replace following line of code:

bookmarkServices["Twitter"] = new string[] { "Twitter", "http://twitter.com/home?status=Add+this:", "&title=" };

with

bookmarkServices["Twitter"] = new string[] { "Twitter", "http://twitter.com/share?url=", "&text=" };

This change should be done in file:
~/CMSWebParts/CommunityServices/SocialBookmarking.ascx.cs (line 635)

Then the link should be shared correctly.

As for linkedin - you will need to modify code of the webpart and add linkedin option. How to modify code of standard web part is described here:
How to clone webpart

I will create a requirement to add this functionality to default web part.

Best regards,
Ivana Tomanickova