Lets say the buy and sell prices are at $110 (plus or minus a few cents) per BTC.
If you use a "limit buy" order above $110, it will ask if you are sure (since this is above the market price). If you say "ok", then your order will be executed right away.
However, the functionality of the "limit buy" order varies with the price you use.
If you use a "limit buy" order at $111, it will buy at a bit above $110, just like the "market buy". This is useful when MtGox is lagging.
If you use a "limit buy" order at $112 to $126, it will actually buy bitcoins at these prices!
If you use a "limit buy" order at $127 or higher it will change your "limit buy" order to a "market buy" order automatically.
This happened to me. The price of bitcoin was $110. I put in a "limit buy" order at $120 and it charged me $120 per bitcoin, despite the fact that there was over $1,000,000 of asks on MtGox between $110 and $120.
Do not use
bucket shops. Do not send money to people who are known thieves (yes, the codebase they use is stolen from Bitcoinica). Do not send money to people who
owe more than they own. Do not send BTC to sites coded in Ruby. Do not send anyone any BTC before
doing some basic research.
