This is pretty useful and I can never remember the exact syntax, so here it is for me (and now you) to remember.
In a Google spreadsheet, you can do an online currency conversion that looks up the exchange rate in real time, making my life much easier.
For example to get EUR to GBP just type
=googlefinance((”CURRENCY:EURGBP”))
(note: [...]

One of the things I often need to do is to calculate the number of work days between 2 dates in order to calculate billable days. There is a very useful function called NETWORKDAYS which does exactly this. It works the same in both Excel and Google Spreadsheets
The syntax is =NETWORKDAYS (start_date, end_date, [holidays])
example =NETWORKDAYS [...]