Any idea why this transacton won't go through?

[CurbsideProphet]

I can receive BTC's just fine but when I tried to send, it's been stuck on 0/confirmations for days.

Status: 0/Unconfirmed
Date: 07/11/2011 17:51
To:16U6zvTH3UKP8EHT6mPZod8C2FrS4oVyy5
Debit:-0.25
Transaction fee:-0.0005
Net amount: -0.2505

Initially I tried to send it with no fee (the client default).  It prompted me if I wanted to pay the fee, and I clicked yes.  Since then its been stuck on unconfirmed.

Edit:  Now it's at 2/Unconfirmed so at least some progress.  But any idea why it took 4 days to move?  Do I need to up the fee?  Leave the client running longer?