I just returned from a multi-week trip around Europe, and used the N900 as my sole device while there. A few pointers from that trip:

I found most wifi places worked well, and the stock browser could do just about anything. I have FireFox and Opera installed, but only had to use Opera once the whole trip. Most free wifi sites to have a "terms" thing to click though, and you have to do it each time you connect. Auto-reconnect is not your friend with those... turn it off.

You'll probably want another battery. Copying files, via h-e-n/external reader or to/from the internal tf slot takes a while and sucks battery fast. I usually did backups at the end of the day so that after the copy I could plug it in to charge for the night.

As already noted GPS lock time sucks without AGPS. I wound up getting a pre-paid sim for a few euro without data. I would turn on the GPS when on wifi, and AGPS would place me within a few hundred feet. (I was in major cities though, London, Madrid, Barcelona, etc.)

I would advise to also turn off most repositories while attached via wifi. You can turn them on easily when on wifi again, which then also auto-refreshes the database. Then just in case it does hit the data plan with a check it's far less data with all the repositories turned off. You can also set connectivity to "Always Ask", which is a great setting for traveling.

One final bit on images: You probably want to either exclude the folder you're copying pictures into for backup via trackercfg, or at least tweaking it to only index while on mains power. If not, it adds tons of images to your device and it sucks power at random times to thumbnail them. If you're copying via the internal slot at night when it's plugged in, that's less of an issue. In that case you probably want to force it to index right after the copy by opening the image viewer. Nothing sucks like showing a friend a picture on the N900, and an hour later having a hot brick in your pocket beeping about low power.

Safe travels!