The SI1520 is light enough to be brought along during a trip.
If it's a car trip, it might even come in handy, as it can be used as a GPS navigator. Of course you'll need a GPS Antenna, which nowadays can be found for just a few dollars on eBay. You can choose among USB models and -just a little bit more expensive- Bluetooth ones.
I've opted for a 32-channels Bluetooth Antenna (made in China and named "iBlue 737") which is very powerful, fast and precise. Also, with its 32 channels, it can reach way more GPS satellites than the antennas with 24 or less channels do, which means you will lose signal very rarely, even when surrounded by high buildings, like in Manhattan. :-)
Anyway, this little thing works perfectly in combination with the SI1520 (I only used it with Windows Vista, since I don't know of any mapping software that runs on Ubuntu) and Microsoft's Autoroute 2007 (for European roads) or Streets and Trips 2007 (for US/Canada roads).
If you prefer, you can directly buy the version with GPS included in the package. It both exists for the US/Canada roads as well as for Europe.
Using these programs, which both support GPS Antennas, you will be able to use your laptop like a GPS navigator. You will be able to create itineraries, and to receive exact instructions about how to reach every destination.
A little investment (around $70) and you will add a very powerful function to your SI1520.