Global Variable Across All Machines?

I'm focusing on Networking programming and I had found something that was very interesting to me in Remoting, which is the ability to have some how a "shared global variable accross applications" ... Here's a quick example of what I'm saying (which is stripped and modified from one found example on internet):

In the Remoting class:

Code:Namespace remoteclass Public Class xx Inherits MarshalByRefObject
Public Shared_Var As String 'This is our share variable
End ClassEnd Namespace

[Code]....

I found that I can eaisly use this red-marked variable (Shared_Var) acrross all application clients without any extra line of code to update its value ... without using even what is called "singlecall" and "sigletron".

But I have concerns:

1) This is only applicable for simple types of variables (e.g. string and integer) but an array or DataTable for example are not updated! and I don't know why!!

2) Would that load the communication network (I mean the content of these shared variables (few KBs to 1MB) will always be communicated across machines all the time without any management) ... Actually I don't how this works from inside, Does it update on change or cyclic ...

3) And finally, can I found something like this in WCF?