"I wonder how can it be called a free and open source software"
At least one of the "requires account" features is a free online backup of your config... which isn't possible without a registration of some sort to allow recovery. That's the same as Jolicloud's Netbook OS distro, which I'm pretty sure is offered by some other distros too.
On the spectrum, ClearOS probably has more in common with RedHat than CentOS. The more pertinent question is that of the "ClearSDN" services: content filters, anti-SPAM, IDS, OS/App, A/V, and various other updates/services. This is a *big* difference with some of the other distros being discussed, and while the prices are *very reasonable* the implication here is that your ClearOS will not stay as up-to-date without these services as the other all-free distros. Maybe I don't know my lingo well enough, but I don't think any of this disqualifies ClearOS as F/OSS,
That said... there is a killer feature in the ClearOS gateway layer that nobody has discussed. ClearOS can do MultiWAN (so load balancing/failover between two WAN/Internet links). That is a very hard-to-find feature without stepping into Enterprise level network hardware - for a SOHO it's either ClearOS or some of the Cisco (rebranded Linksys) "Dual WAN" devices that, from what I've seen with them, don't seem to last too long (especially with their 4-Port don't be surprised if you have to replace it after a year). I'm a big fan of ClearOS as a Gateway for SOHO.