Trying to find out what people are using for Firewalls(Software/Hardware) with their VPN(remote users)?What good/bad experiences have you seen? What would you not recommend?

I just downloaded the Certicom client on an IPAQ and got it to work with the VPN-3005. Only two things that I found that were any different than the Cisco VPN Client were,Can only do internal authenticationIPSec - IPSec SA - has to be changed to ESP/...

If you have a PIX-525 running as your Primary Firewall can you use a PIX-520 or PIX-515 as the failover for this box? If so, any special requirements?