Unless you need SSL, then the free service is pretty good for everything else - use it as a free CDN and you save in traffic.
If you need SSL proxying then $20 a month for PRO is not bad. The $200 a month for enterprise is too much for small businesses/websites, but it can be good for some larger companies.
As I said, still use it for the CDN on my domain. I used DynDNS and MaxCDN before but Cloudflare came with a closer node to our main readers, so switched. Also MaxCDN doesn't support SSL (for cheap).