Really like the look of the site very easy to navigate and understand. Obviously the concept is also amazing as well! Two notes that I think hit me off the bat.
-The testimonials page I thought was pretty weak and maybe even not needed. As a feature button on the top of the home page I expected way more substance or you might want to replace it with something all together - like with a featured success story page and spotlight your best fundraisers every month or something like that. Or even a video page as someone mentioned in the top testimonial.
-The site seems like it has no way of preventing fraud. How do you combat fake fundraisers and people just scamming the system? There maybe should be more on the how works page about what you do to handle these types of situations. If someone used your website as a scam and that got out it could really hurt your business/image and the least you should is mention that it is not tolerated and you hav preventive measures in place to sniff that stuff out.
-You should play up the crowdsourcing card more. Crowd sourcing is a huge trend now a days and is basically what your site is but there is no mention of it anywhere on the site. The crowdsourcing angle is a good angle to play for a service like this.
-You should try to contact as many legit organizations as you can and try to have them make a page. Also you might want to have partner charities that have an on going page that never ends and then featuring each one on a rotating schedule.
Keep up the good work it looks awesome and is a sweet use of technology. It looks like you are helping lots of wonderful people and causes.