1) ^\s is equivalent to \S

2) Just because you can do something doesn't mean you should. The delimiter ! is a horrible choice.

3) I think this would handle the case you mentioned:

s{(www\.)?(\S\.com)}{<a href="http://www.$2" target="_new">/>$2</a>}
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4) Don't try to reinvent the wheel. If there is a module that deals with all the intricacies of parsing something, use it.