I like the Gingerbread keyboard because it doesn't seem to automatically add everything I type that it doesn't recognise to the dictionary. Whenever I typed something the Sense keyboard didn't know, it added it to the dictionary. Sometimes I type a lot of character strings that aren't words and I don't want them cluttering up the dictionary. There was no way of switching back and forth between predictive and non-predictive whilst typing.
I don't think that the Gingerbread one does this - or at least its not telling me that its doing it (the sense one always used to say 'xxxx added.' That said, there must be some mechanism for it to add new words, so maybe it is just doing it without telling me...
Al.