In addition to the many great suggestions already made, here are two 
more:

* Many things that you're used to thinking of as syntax are now just 
code.

* For good (but subtle) reasons, you have to leave the '++' and '--' 
operators behind.  You can still use '+=' and '-=', though.

Although I understand the reasons for that last one, years of C, C++, 
Perl, and Java still lead me to try to use them in Ruby every now and 
then.

---Glenn