Heh, I started out on bass (5-string) and have been learning guitar the last 2 years.
As stated by others, one of the most "annoying" things is the G-->B string. I still get thrown off when navigating around the first 3 strings and reverting back to my "bass" scales. So I need to make sure to practice scales on both instruments.
Another tricky thing for me to is how my 5 string has B as it's lowest string, but my guitar has E as it's lowest string. It hasn't been too bad since I started off on a 4-string bass for a while before moving to a 5-string bass. But it's another thing to think about.
Lastly, if you don't use a pick on bass, that takes some getting used to for playing guitar with a pick.