Checking emails, and doing some normal web-surfing shouldn't be too bad. Its when you get into some downloading, or streaming media content that 5GB of transfer shrinks pretty quick. Also lots of flash websites, or other web2.0 interfaces tend to suck up more bandwidth than good ol' HTML. If you do get the service there are many downloadable programs that can track your usage so you don't accidentally go over the limit. The ISP may even provide one.