I use regexes very frequently to filter search results, and I do that
because I can achieve things that I cannot achieve with substring
searches. I think it would be great to have regex searching in the
client, because then fewer relevant search results would be dropped
because of UDP packets being discarded by my modem when my bandwidth
is breached.

I don't understand why it matters whether the majority of users will
be able to use regexes or not. Since regexes allow a set of achievable
search criteria that is a strict superset of that which substring
searches allows for, without sacrificing almost any speed (see below),
it is, quite simply, very, very good.

I agree. That's clearly what defines a power user. Not everyone has the same usage, why do you want to limit the "power" given to users ?

As someone mentioned earlier on this list, regexes _are_ available for
Windows from http://gnuwin32.sf.net/. I don't use Windows, so I can't
give any specifics, but I guess that it's a library that can be
directly included in the source code for a program, just like, for
example, bzip2 has been included in DC++.

that's a very good reason (and the regex processor should probably be a single file with a ridiculously small size).

Considering how regexes are available as a seperate library and all, I
don't see how using regexec() instead of strstr() makes it so much
more complex. In that case, I'd say that eg. filelist compression adds
much more complexity, wouldn't you agree? It is nonetheless very
useful, just like regex searches are.

Moreover, it won't be strstr because windoz loo^H^H^Husers won't understand why if they search for "toto", they don't receive files like "Toto", "tOto" or any other possible case sensitive changes.

Eric