I used lensrentals.com for my WDW trip just a few weeks ago - it was amazing! I price-compared with borrowlenses.com and a local shop, and lensrentals.com was the lowest.
I didn't have to rent any extra days to have it arrive at my home. I had it shipped to Old Key West (my resort) for arrival on the same day we arrived (when you rent online, you specify what day you want it to arrive at the location, and they guarantee that arrival date) and when we checked in at 6pm, we just asked the front desk if it had arrived and they brought it out from the back. I had it arranged to be sent back on the day we checked out. It came with a prepaid shipping label, so we kept the box and stuffing it came in. On the day before checkout, we called FedEx to schedule a pickup for the following morning, told them we were leaving the package at the front desk. Then the morning of checkout, we took the box to the front desk, asked for some packing tape, packaged everything back up and slapped the label on. Everything went smooth!
Just to comment on what others are saying - I have a Sony NEX 5 and the reason I rented was because I wanted to try out a telephoto lens. It cost me a little over $60, inclusive of both-way shipping to rent the lens for a week. This lens retails for $349, but it was just not an option for me to purchase it. I paid the $60 and don't regret it at all - got some great photos! I think it really depends on the photographer, camera, and lens, but you don't always need to tinker with the equipment before hand to "get used to it" before your trip.
Good luck!