I've got a domain registered with some domain registrar, and on the configuration the namesavers are those of that registrar.

But on several howtos it seems that people recommend to change nameservers to the linode ones (ns1.linode.com and so on), and then go to the DNS Manager on your Linode account and add a new domain zone with the proper domain you have registered with your registrar.

Does this make a difference in performance? Can my site be unavailable during the DNS propagation?

No, it doesn't make any difference in performance unless the nameserver you're currently using is horribly slow.

In most cases, it's really just a matter of preference. Some people prefer to do the DNS on the registrar's side, since many registrars these days offer DNS service. Others prefer to do it on the host's side -- this is standard practice in shared hosting. Still others will purchase DNS service specifically from a third party, or run their own DNS server. But it all depends on which way you prefer and the quality of the respective services.

Unless you're looking for features that are not offered by your current DNS service, or the service is crappy in general, there's no need to switch. Having everything in one place makes it more convenient, though. And Linode's DNS control panel is better than most others.

Good to know. I don't really need anything else from what my current registrar gives me, so I guess I'll stick with the current config.

Cheers!