Thought I'd better start a new thread as we've drifted so far from our 
starting place!
@john lewis - I can't understand why TiddlyWiki's not working for you 
with Opera, to quote the TiddlyWiki.com homepage:
#  Ability to SaveChanges on:
    * FireFox under Windows or OS X
    * InternetExplorer under Windows
    * Opera under all operating systems
    * Safari and Camino under OS X
    * Minimo on Nokia 770
So it looks like it should be OK. 
As to modifying it on line: TW uses JavaScript which tries a mozilla 
method, then an IE method, then a Java method in turn. I guess most 
default hosting environments would disallow those actions (JavaScript 
being allowed to write to your website seems a bad idea at first 
glance!). If you want to keep the master copy on line rather than on 
a memory stick or your hard drive there is a host at 
www.tiddlyspot.com which will get you up and running with an on-line 
TiddlyWiki (either public or private) instantly. 
Personally I put it on a memory stick so it's with me whether I'm on 
line or not. I then include it in my sitecopy config so a (read only) 
copy is synced to our website in the normal course of things.
HTH, Peter