Just one example, I carried out a transfer using Dwolla to go from my bank account to Mt. Gox on Wednesday night, and the Dwolla site projects the transfer to be completed on their end by today (Monday) at 5pm. That's three full business days, not including the fact that there's been a weekend in between.  Current status? I still don't see it in my Mt. Gox account.  Considering that MagicalTux has to manually enter a spreadsheet into his system until Dwolla changes their system to automate it for him, it probably takes an additional day for that to happen.  So I guesstimate at least 4 business days total.  You better get your transfers in on a Sunday or Monday morning, or I doubt you'll see it until the following week as things currently stand.

May I ask how much? (ballpark figure) I ask because maybe they have a certain transaction threshold or something? Mine still hasn't posted on Mt. Gox, and it's still pending over at Dwolla.

Dwolla is a cash service.  Getting cash into dwolla is what takes a long time.  From there, sending the cash already sitting in your Dwolla to either Mt. Gox or wherever is fairly quick.   Technically, it happens instantly -- Dwolla's debits your Dwolla account for the amount you sent and then credits the Dwolla account to whom you sent funds.

Now, the method that the exchange uses to then credit your account at the exchange with the funds received will vary per exchange.  

Mt. Gox processes Dwolla transactions hourly.
  - http://en.bitcoin.it/wiki/MtGox#Dwolla

But until those funds are in Dwolla (which you can easily monitor by logging into Dwolla), there is nothing that Mt. Gox can do about it.

Looks like the hold up was Dwolla.  It finally went through at 5 pm today.