If i understand you correctly, you dont want ppl who you pm to see your host? You do realize that can be seen when you join a channel, or if someone does a /whois on you, not just when you pm? Be aware also that if you use a bounce, while those online with you wont see your real host, the person who runs the bounce (also a total stranger) can see not only it, but there is the capability to see everything you type, including your passwords?
I think many ppl use a bnc to get up to no good or hide something or just to have a cute lil host than for any perceived security reason.