So, I assume that if I use a write-protected usb drive, I should be safe from viruses and malware attacking the usb. 

Then I would be susceptible to keyloggers and screen watchers.  However, if I use an on-screen virtual keyboard, and software that blocks screen watching, would I still be vulnerable?

I will be traveling without my laptop and was planning to bring a USB drive with portable apps including Firefox and a VPN client. 

If I run these applications from my USB drive in a public computer in a lobby or Internet cafe, will it leave traces of personal information that I use to log into accounts on Firefox (e.g., gmail other web mail, or OWA)?   I also was thinking of connecting by VPN to my employers servers.  How safe is all this???

Thanks,
jdd
 

My experience is that it takes forever to upload files of any substantial size using a cable Internet or dsl connection, which is what I have.  How can you do that effectively without FTP?  Am I missing something here?