I use CadRail 8.0 and have had it installed so long that I don't even recall what it cost. Given that amortization, it's been worth it from a monetary standpoint.
Regarding using design programs in general, I like them for exactly the reasons stated above: keeping curves and grades honest. I've also found that having a to-scale drawing has been tremendously useful for other projects that require space planning; again to keep me honest.
My father is an architect, and my brother is a graphic designer (I'm in IT), so they of course point at me and laugh regarding using a CAD program for my rough layout planning. While CAD is becoming very common in architecture, dad is one of the last guys in our area that does almost all of his work by actually drawing and can put a knock out a conceptual drawing in - literally - minutes. Being that both are railfans, they are able to sketch out decent track plans in no time flat, and if this were their layout, I'm sure their process would be much closer to what DoctorWayne and Fred describe. I however need the hand holding that a CAD program provides. We as a team have come to terms with this - the sketch, then I draw up a couple "master" cad drawings to use for the next iteration of planning.
To your question. I've been using CadRail since at least 2000, and once the basic tools are located and mastered, the work is very pretty straight forward and quick. That said, selecting said tools can be kind of clumsy, requiring a lot of mouse movement to accomplish. For example, drawing a curve or line requires two buttons and the drawing action itself to draw freehand. To do the same to place the same item at a given elevation, grade and radius requires three tool (button) selections, a dialog setting for the radius, the drawing action itself, selecting the item, then clicking two more buttons to access the edit tool to adjust elevation and grade. It gets very quick after a while, but is a busy process nonetheless.
Sizing (zooming in and out), and scrolling around the plan is also somewhat clumsy. Not hard, just old-fashioned feeling in this day and age of scroll wheels, dragging images around with the pointer, etc.
The usability issues may be better in version 9, but I haven't looked very closely at the release notes or tried it out, so cannot comment on that. I'm happy enough to use v8 for what it is, since the program and I now understand one another. But if I were to start again, I wouldn't hesitate to give the all the freebies a try. Just beware that all will require a learning curve to get comfortable with, then another curve to become productive, and a third (optional) curve to use all the bells and whistles - but it sounds like you're cool with that.
Full disclosure: (to Fred and Waynes comments) I've been planning my next layout for 6 years, though that isn't due to any particular love of CAD...
Matt