Blatant self promotion - I wrote a little bit about this on the superuser blog.
Now on to your points:
These backups takes some time and nothing I would like to run everyday / all the time. Is there some nice software that "realtime" backups my laptops everytime Im on my home network, or should I run a file backup once every hour and set a disk-image backup one a week?
Real time backup is quite a difficult thing to achieve - to do this, as a developer you need to intercept changes to files or folders. The long and the short of this is that doing so adds a processing cost to every write operation as you must now check what has changed.
For small amounts of data, this is fine (e.g. Dropbox) but you start to run into problems with say whole disks.
Now, you might ask how disk imaging actually works and the answer would be copy on write. Basically speaking, a temporary space is stored and whenever files change, a copy is made of the original in this temporary space (the original being written to disk). This way backup software can access the file as it was at a given moment in time, without having to do any comparing or additional work. This is how VSS services work.
Anyway, clearly, even with differential/incremental backups this is going to take some time. I guess the question you have to then ask is how much of your system requires backing up in realtime, all the time. If you're anything like me, your basic system doesn't change too much, but the data you work on may well do.
In this case, it sounds like what you really need (assuming absolutely critical, must be backed up all the time on every change) documents is a raid 1 hard disk setup. This gives you mirrored volumes which can be disconnected from the raid controller and used standalone, so if one disk fails you still have a copy of the other. You could easily serve this volume over the network and access it from all of your network PCs.
If your data is not that critical, I would suggest a pattern which reflects your use - backups at key changes, along with regular small (incremental/differential) backups daily/every few days and full images weekly (every other week). Basically, adjust timings for your needs.
Finally, RedGrittyBrick's answer get's my +1 for the "testing" bit alone. Absolutely. There is no point doing a backup if you cannot restore from it.