I don't know what happened, but it worked a little bit more each day...

Now I can ssh in from both my home connection and work. I didn't change anything, I didn't clear anything, I just rebooted the phone daily (as I'm already wont to do).

Thanks for the help, even if there wasn't a specific fix. I'll post back again if it acts up again.

I have had a similar problem, sometimes the wireless interface decides to go to sleep a bit too much and I need to have a ping running on the n900 to the host (or the Internet or anything), and then it works.

Other times it works fine without anything running on the device (I checked, even the weather isn't updating).

If this help the next time it doesn't work, then in the network settings, in the advanced part, go to the "other" tab and play with the powers savings tab (or just use a ping...)...