I'm sitting here pondering the same thing. There are a lot of positives about the phone (my personal favorite being the fact that I can mount the phone as a disk drive and access the ext SD card WHILE downloading apps to save to the internal @ the same time), and the responsiveness is nice as well. It's also encouraging to see that it's going to receive a lot of developer support in the coming weeks and months.
But, like you, I am also fresh off of the 3D, and married to the charger as well. With less than stellar Sprint service @ the office (.1-.3Mb down avg) and avg (.5-.7Mb) @ home, I'm looking at about 10-12hrs of moderate usage off a full charge. I wasn't expecting miracles w/ the Evo LTE, but with the bigger battery, I expect @ least 12 hrs w/ moderate usage alone, and total batt life of around 16-18hrs. This isn't unreasonable, as many, many reviews have reported.
Perhaps the batt. will settle in, as I'm only 48 hrs into the phone, and have already rooted, tweaked, etc., so I expect wonkiness until I let it just rest and "learn". Additionally, I'm not entirely sold that returning this phone and holding out for the S3 whenever it's released is going to be the best bet.
So I'm torn. I'm already accustomed to keeping a USB cord handy whereever I go, so it's nothing new. But I feel like all it'll take is one major glitch for me to dump the phone and make a move to the dark side (have been HTC loyal for about 4 years, haven't used a Sammy since the Instinct days lol).
(shrugs)
**EDIT** - Almost 2 days after letting the phone settle post-flash and script modding, I can report that the battery is holding much, much better. Will be looking @ about 20 hrs w/ moderate usage. This, combined w/ disabling Rosie, has made the phone a keeper (barring any major glitches, of course!)