Subject: Are there situations that quantum computers cannot handle?

From what i've read, quantum computers could be extremely powerful compared to 
conventional ones, however, from what i understand, they would be limited to 
tasks where you want to compute several possibilities.

If one was to encode some data using a quantum computer, i understand that you 
would end up with several different copies of it in the encoded form, the 
number depending on the size and number of variables involved.

Another thing i was wondering was would a quantum neural network work? I cant 
see how it would. Yet i think that combining the power of neural nets and 
quantum computers could be very useful.

thanks for your help.

Re: Are there situations that quantum computers cannot handle?