The & character is also used in Google Analytics parameters. I believe that if there were any problems they wouldn't use. I use this character only to inform the start and finish parameters.

A good example is the UTM parameters used by Google: http://www.domainname.com.br/?utm_source=yourdomain&utm_medium=algo&utm_campaign=yourcampaign&utm_content=something

If you need to include special characters as the information is interesting escape the text before sending to the server.

http://someserver.com/?param1=someinfo¶m2=another¶m3=some text using special characters such & % and more

The url can be correctly corrected using the javascript escape() function to convert special characters like:

var param3 = 'some text using special characters such & % and more';
escape(param3);

// will result some%20text%20using%20special%20characters%20such%20%26%20%25%20and%20more

So your URL will be:

http://someserver.com/?param1=someinfo¶m2=another¶m3=some text using special characters such %26 %25 and more

..And will be corrected.