Derby v SQLite

In another thread I recently wrote "I'm happy with the way that Derby  
has behaved, but I'd like to ask a provocative question nevertheless..."

Back in the summer, when I told my son (who is a computer  
professional) that I had a Masters student porting my MySQL db to  
Derby, he told me I should be using SQLite, which is what Google is  
using in its Gears thing. I persisted with Derby, mainly because it  
is Java and my app was in Java, but I'd be interested to know what  
people regard as the relative strengths of weaknesses of the two  
embedded DBs.

David