The accepted way to install applications is using repositories. I found this list: http://www.gronmayer.com/it/index.ph...&system=maemo4
But I'm unsure how stable or reliable they are and where which applications are.

If you access Nokia's OS2008 user site from the tablet you'll see featured downloads. There are downloads on maemo.org and on some developers' homepages. Those are (deb) packages, not repositories. Sometimes a repo is mentioned in the package description or in this forum.

Is the right way to install sw on the talbet to google for a repo and hope it will be well maintained? Or is there anything better? Like a community or Nokia managed central repro of "approved" or "known stable" or "end user ready" packages?

If not, what's the big deal of repositories. (Technically, I can see the repos makes distributing upgrades easier, but to be helpful I need to trust the repo maintainer. I don't neccessarily want to install any available upgrade, especially with beta software.)