Some minor problems with VB Apps:

Lack of multi-threading:
Causes problems if you get into a long process that doesn't give
up processor time to update the UI (DoEvents). In an app such
as this it would be more of a problem than usual. If you carefully
create your functions it can be overcome easily.

Dependency Files:
Large runtime files that have to be distributed with your App.
Can't really get around this unless you make to distributions of
your app, one with the runtimes and one without.

API Calls:
Depending on the function some API calls can block not allowing
your client to update the UI. This can be avoided by simple
testing.

Winsock Control:
Simple to use and no REAL issues with this type of app. You
could look for a better one. Gnotella used a different winsock
control (library) but I can't remember the name but it might have
been a custom control.

There is no reason you can't make a client using VB. The
limitations I mentioned above all have some type of workaround
(except maybe the dependencies). The examples on gnutelladev
(at least the last time I looked) are quite old but could be used as
a generic example.

You could write it in VB.NET but then your dependency files would
become even larger (Look at Swapper), but all of the problems
above disappear. If you know C++ that would be of much help
because you could write a library or control to handle alot of the
things VB is not so great with.

Even though many people claim that VB sucks it is damn good at
making programs. There are still people who claim Gnotella is the
best client ever written, just visit the Gnotella forum.