I have used both Telus and Bell EVDO 3G cards. Fortunately, work covers the $100/month "unlimited" data plan. It also helps that our company pools data plans across all users. I know i've crossed 10 gigs in a month and I've never been busted. On a consumer plan though, that would've been a $800 bill.
Please keep this in mind... It should not be used to replace conventional internet connections.
there are two nice features on the bell service over Telus. Bell's connection software will track you upload, download, and total data transfer during a session. Unfortunately it also wants to manage all your wireless connections. Bell also gives you access to what they call HotSpots. If you are at a Second Cup for example, you'll see a wireless network that you'd be able to connect to using your Bell credentials. Though this is done with any Bell account, the rocket card helps expedite the process of connecting.
Connection is remarkably fast upload and download. Comparable to a 3-5mbps DSL connection for download. I've used mine for ridiculous uses... transferring gigs in a day, pushing content to remote FTP's, remote database access (Citrix) , office VPN tunneling, video conferencing, skype... you name it, I've done it on the card.
Because so much of my work is done out of the office and electronically, it is a must have tool. I had the choice between a BlackBerry or an aircard. Very glad I took the aircard.