Photoshop Etiquette rule 41: compress your PSD files
The Photoshop Etiquette Manifest is something every web designer should comply with. In addition to its 40 excellent and straight forward rules I give you rule 41:
Always compress your PSD files before delivering
This significantly decreases the file size, from what I've learnt approx 20–50%, and keeps everybody else's Dropbox/Basecamp/email accounts more slim.