Was wondering myself. Probably yes if your friends/fans are the same people.

actually I have seen many peeps rePlurking/Tweeting things... I did a few times to judge conversation rates

I don't think so. I think using both provides a way to spread your message even further. Sure some people will see it twice, but oh well.

I am in complete agreement with mwilton13, just pull the rip-cord on both and get as much feedback as you can

nah but lot's of questions on plurk arent' relevant to Twitter as it's too hard to keep a convo going. I'd double tweet announcements fo sho

I use Ping.fm to Twit and Plurk from one place

isn't that what ping.fm was created for?

more than just those two, but yeah