We were going to use a stroller from DLR...but we found they weren't extremely easy to use.
You cannot take it outside DLR/DCA at all. So for $15 a day you can only use in the resorts.
We actually ordered a stroller to our hotel suite for a total of $15 and then we regifted it to another family (Diapers.com - free first delivery). We had 12 days and we could use it anywhere...you could also go to Target which is a short city bus ride away (10 minutes I think) and choose a cheap double stroller.