It's been over a month now that I've had my t450s and I thought I'd provide an update.
Overall I'm very, very happy. Once I got the Crucial BX100 500GB installed performance has been excellent. I have no problem opening typically laggy apps such as Coreldraw, Sony Vegas Pro, Adobe Photoshop Elements 13 and the like. They open in less than 5 seconds. Overall "snappiness" isn't like my 4770k of course but it's very close.
I've learned my around Windows 8.1 and made some customization adjustments to the trackpad so I'm getting along with it much better. I also picked up a MS Sculpt mouse which I love. It connects to the t450s via bluetooth so no don't hanging out the side of the laptop.
Battery life for my typical usage, Chrome, Word, Excel, maybe some Photoshop Elements, Sony Vegas Pro, and Microsoft Web Expression 4 is around 4 to 5 hours and depending on how bright I keep the screeen and I keep it bright normally.
The one strange thing I've noticed is that the external battery, which is used first will drain all the way down to 5% or less before the internal battery takes over. Seems like it should switch over around 25% as Li Ion batteries will have a much longer lifespan if they are not deeply discharged. But then I guess Lenovo wouldn't be able to sell as many replacement batteries. I suppose the upside of this is that the internal battery should last quite a while since I rarely "get into it."