I'm not sure how long Twitter is going to remain a useful source of information. More and more, it seems like it's being flooded with nonsense: either nonsense from spammers hoping to make a quick buck, nonsense from barely-concealed Iranian government proxies, or nonsense from well-meaning folks who are retweeting whatever catches their eye, without an eye to its veracity. Already the #iranelection tag is deprecated, and it seems to have split between several others. (I won't post them, just in case, but following key Iranian bloggers like Persiankiwi will reveal them.) If this keeps up, the white noise will make the whole thing useless.
I'm just a humble blogger, so all I can offer is advice: if you cannot contribute to the discussion, leave it be. Twitter is a participatory medium, but hashtags are a ramshackle organizational tool to begin with, and your attempts to show your support by adding them are just going to make it worse. If you want to show your support, by all means tweet (or twitter or whatever) your support. And if you seriously think that something deserves a "re-tweet" and hasn't been RTed in the last while, then do it.
Edit: If you do re-tweet them, strip out their names. I know you want to credit them, but you could be endangering them. So don't do it.
But otherwise, let the people of Iran get the word out. This is their story. Not yours.