I picked up a Dell Streak as a companion device to my n900. Thanks Fonebank £260 for 3GS. I use the streak for Google Maps navigation, browsing and various alternatives to n900 functions. The best of both worlds. A nice ssh tool ConnectBot and c:geo for Geocaching.
I love the n900, it is and will remain my primary device. If it was a choice between the 2 it would be no contest. However, for train journeys the n900 and streak combination removes the need for a laptop or netbook.
On the storage side I have 32GB in the streak and 48GB in the n900.