My only concern regarding rain dispersal systems are that it doesn't really move the water away from the foundation. It won't clog, which is great if your house is surrounded by great big maples or something, but gutters do an important job of moving water away from the foundation and away from your crawlspace.
Now, I bring up a fun topic, which you can read about on this board over the past 3 weeks or so. If you live in some strange area of Texas, where apparently they actually bury soaker hoses around the foundation to keep the soil damp, ignore everything I am about to say. On the other hand, if you get more than 20 inches of rain annually, (90% of the US does) then consider this:
A house that does not get water away from the foundation, but instead directs the water under the house, undermines the soil, making it soft, inducing cracks and all maner of structural headaches and nightmares over a long period of time. If any of this water ends up in the crawlspace due to inadequate sloping of the surrounding yard (it needs to slope AWAY from the house for at least 10 feet and have someplace constructive to go) you can end up rotting out your structural beams, posts and joists. This is a BAD thing.
I can't speak for your particular situation. I don't know how much rainfall you have, what kind of a foundation you have, or what your yard looks like. I haven't seen exactly how good the rain dispersal systems are at dispersing the water and getting it away from the house, but I can say that the yard slopage is CRITICAL in this system. This means no landscaping "berms" around the house that trap water between the berm and your foundation. You have to have good slopage.
Jay J, and BC, quit your laughing, and Gutterless, I wrote this JUST FOR YOU!