VPN and firewalls

[Rik Farrow <rik () spirit com>]

I am curious about why people are choosing VPN solutions which
are independent of firewalls, for example, Aventail or TimeStep.  

Do people poke these streams through their firewalls?

Is it a matter of performance?

Why pay extra for VPN capability which is already included in many firewalls?

What products are preferred and why?

I am looking for answers from people who have tried both methods:  using
the VPN as standalone product or bundled with their firewall.

Regards,
Rik