Have you found Power-Over-Ethernet to be an effective solution for the enterprise?

I don't know about the standards changing for PoE, haven't heard of any issues there. We run many Cisco VOIP phones and while we do have some issues (the phones are basically computers; they do lock up and resetting them is a matter of unplugging and plugging them back in) we haven't have direct issues due to PoE.

If you don't have PoE switches you have to plug in a power injector or a power adapter on the phone.

Taking VOIP phones...on the road? These are desktop phones, usually. I mean...do you have a lot of people taking their desktop phones with them on the road? If it's a portable phone, it's already got mechanisms for being carried...just like you already would have to do. Or they use cell phones.

PoE does work well for remote WAPs as well since you can reset them at the switch and it's less cabling (just ethernet instead of ethernet plus power).

I'd say that yes...it is effective at the enterprise level and investing in PoE switches is no more dodgy than installing any other technology available today.

plugging in a non-PoE switch in front of a PoE switch will mean that all devices under the non-PoE will not have power

That ^^ would be correct.

PoE switches in the enterprise are really becoming the norm now, especially edge switches. The cost differences are pretty minimal at least with the big players like Cisco, HP, Extreme, etc.

WAPs, VOIP phones, server cameras, etc. can all benefit from the ease of PoE switch ports. Most switches that have it are "auto-sensing" and will automatically apply the power if needed.

I would say it is "more effective" at the enterprise level than elsewhere. Small deployments can get by with power bricks/adapters but for large scale it ends up being cheaper to go with PoE switches then to buy power bricks for every PoE device.

For VOIP phones on the road, yeah you'll need a power adapter, but usually it is easier to just use a softphone app on a laptop that connects over the web to the enterprise PBX (remember you were asking what enterprises do).