I rarely use my ebike for three reasons:
1. The commute is just too long - normal commute is 15km per way, which is just within my personal limits, but I'm currently at a satellite office 20km from home, so you're looking at an hour all told from front door to office door on my pissy little 250w motor which is all that is legal here, as opposed to 45 minutes on public transport. Half an hour a day adds up... That on its own wouldn't be too bad, but for 2.
2. The bike path is too damn bumpy. Don't be a fool like me and get an ebike with no suspension. Your arse will thank you for it.
3. I'm shitty with maintenance and repairs, so when something breaks (which it does every few months, especially spokes thanks to 2) I have to take it into a shop for repair.
If these apply to you, I'd say an ebike is a bad idea. Not because it's a bad machine, or that you're a bad person - it's just a tool which is not suited for your needs. An ebike was much more suitable for me at my last job, when my commute was 9km per way, the way wasn't too bumpy and the public transport was terribly slow.
I reckon an ebike is a great choice for a commute up to 10km per way and a reasonable choice for up to 15km per way. Beyond that, you're better off taking public transport or just sucking it up and driving. Moving closer to work would be the sensible choice but I get free rent here, which compensates for the cost of taking PT. ^_^
I don't agree with the comment that an ebike is worse than a normal bike because you get less exercise. You may get less exercise per trip travelled, but you are a lot more willing to stiffen your (mustached) upper lip and get on the bike of a morning because you know you can take it easy and let the motor do the hard yards. You'll still get your wind up, I guarantee it. It's also a great way to get over a work day - by the time I get home after work, yes, I'm tired, but usually in a better frame of mind than when I left. It's hard to be angry out in the open, tunes in your ear, wind tugging at your clothes and you breathing fresh air deep in your lungs.
Locks: I use a u-lock and a chain lock. U-lock secures the quick-release wheel to the frame, and chain lock secures the motor wheel to the frame and an object in the environment. While there's a chance someone can use bolt cutters to get the bike free, they would need to carry it somewhere they can remove the U-lock, so I figure that's deterrent enough. Obviously you can't prevent someone who's really determined from nicking your kit, but if you are paranoid I think you can buy chain locks with an integrated alarm which would provide a little more dissuasion.