You can only take out max $1k per 24hrs in either Bitcoin or $$$ due to lame US laws (maybe Japan law too?) unless you send ID scans to their compliance email address
I did not withdraw money or btc in a month. And now I can not withdraw even one btc. It turns out that my limit is not $ 1000. My limit - 0.
I'm not sure (since I sell BTC, rather than buy it) but I remember hearing in these forums that Mt Gox has a waiting period for withdrawing BTC bought with brand new funds. The idea is that you need to keep the money in Mt Gox for a few days (not sure of the time period here) so that if there's a reversal on the Dwolla side Mt Gox will have a greater chance to be able to recover the funds.
Perhaps someone with more experience buying can chime in here?