-housing in Geneva is expensive. the best deal is with the CERN hostel in St. Genis, however it gets fill rather quick and a few months before summer they reserve the spaces for the summer students so, as soon as you get your CERN IDs  book it if you know your staying. this will save you hassle and money.

-Also there will probably be a lot of drama with the flights. BU pays for a group flight which leaves June 30th-ish. if you plan to say longer many people found that it was cheaper to get the refund for the flight and book it your self. However, if you know you want to stay during the summer then as soon as you get your study abroad package that has the info for the flight, call up the travel agency that BU has the deal with and have them immediately change the return date. also when you are accepting your flight there is a option to request later return date that makes this process easier.  you can always change  the return date of for a price of course and it gets ridiculous quickly.