So is it ok to use swap or not, because this is not making any sense to me, why would anyone create swap space on systems with zfs and ecc memory if this is the case.
You can use swap if you want to. If your concern is that data paged out to swap space loses the protections of both ECC RAM and ZFS, then I would say your concern is valid. (Data corruption may be unlikely, but it does not make much sense to deliberately make a swap partition that circumvents the protections you deliberately put in place.) The proper way to use swap on a ZFS-based system is to either create a swapfile, or create a zvol with its own swap partition. It doesn't seem proper to create a separate swap partition on-disk, or a second zpool just for swap.
PCBSD's decision to use ZFS by default is an uninformed one in my opinion.
I would have to agree, for pretty much the same reason. Using ZFS on a desktop is just fine, but requires the sort of knowledge and attention not typically found in PC-BSD's target audience.
An other question PCBSD uses zfs as default file system, not one desktop motherboard that I know of even supports ECC memory.
The recommendation to use ECC RAM is just that: a recommendation. Some overly zealous ZFS advocates have blown it out of proportion. The general reasoning is this: if you're already taking the extra step of using ZFS to protect your data on-disk, wouldn't you also want to take one more step and protect it before it's written to disk? If so, ECC RAM can provide an extra layer of protection, so if your data is really, really important, you should use it. But there is nothing inherent to the design of ZFS that makes using it without ECC RAM dangerous or stupid.
Here's something to consider: the most vocal and vehement insistence that ECC RAM (and other really expensive server-grade hardware) is a requirement for ZFS comes from the FreeNAS community. FreeNAS is a server-oriented operating system. PC-BSD uses ZFS as its default filesystem. PC-BSD is a desktop-oriented filesystem.
FreeNAS and PC-BSD are developed by the same people---ix Systems. Thing is, ix Systems doesn't sell a pre-built
desktop system with their branding stamped on it and PC-BSD installed. But you can certainly give them half a month's pay for a pre-built FreeNAS server, complete with ECC RAM.