If you regularly program in Java and C#, it gets really annoying, becuase the languages are so similar it's easy to make mistakes and end up having code that should work in one in the other. Sometimes I forget which way around they are:

C# / Java
string / String
StringBuilder / StringBuffer
Hashtable / HashTable
System.IO / java.io
SqlException / SQLException
.ToString() / .toString()

which are probably right !

(yes C# generally uses more capital letters)