I don't know about how the Pool program is, but Moniker lets you do the same thing if you are a NamePros.com person. Just started doing that today with them today myself.
Send an e-mail to Don Lyons ([email protected]), and ask for the Namepros discount. Send him your user name, e-mail address, and user ID. As low as $6.95 to purchase a domain name, and the ability to "taste" a domain for $.25. The guy seems like a really quality dude, and Moniker is skyrocketing up my registrar list after e-mail him.
I haven't tried either Pool or Moniker but have looked up pricing on both.
Pool has tiered pricing for tasting - depending on the amount you have on deposit with them. A $250 deposit gets you pricing of $.20 for a 4.5 day taste. A $50,000(!) deposit gets you tasting for $.10. Its presumptively a taste - so you have to take action if you want to keep the domain beyond the 4.5 days. Gives you the opportunity to test for traffic. .coms are $8.25/year if you decide to buy.
At Moniker the tasting is $.25 for 4 days and if you decide to go ahead with purchase its $6.99 for a .com. Again a deposit is required to obtain this bulk rate. Not sure if presumed that you are cancelling the domain after 4 days like Pool.com.