LR 3 is the only version I have ever used. If I try LR 4, am I then stuck with buying it to be able to reuse any of the image files I adjusted with LR 4? I really did not want to buy LR 3 after the trial, but it seemed to be the only way I could ever get back to the files I adjusted with it. I never could load them later into Photoshop without having LR installed.
Lightroom doesn't really work with "files" and "changes to files". It works with images. takes your original source data (OK, a "file" technically) and then just saves the Lightroom adjustments you are making to it, separately. So you can't open this without Lightroom obviously.
However what you can do is take all the images you modified in Lightroom, save them as 16-bit full-resolution TIFFs or whatever (basically a 1-click operation using export presets) and then continue editing them in whatever other program you use.
LR4 is the only one I have ever used. I am concluding, based on so much input, that what I want does not exist. I have a 12? step Photoshop workflow that I use for every image. I do just about everything in layers so everything is non-destructive. I always save the file with layers intact. Plus, I like to vary the opacity of some adjustments. My workflow always entails printing an 8x10 proof and saving an 800 pixel wide JPG. Things go quick as I seldom pause to have to think of what a file needs. It takes about 2 minutes per image.
A lot of that workflow seems to be based around complex functions that you need in Photoshop to work around the inherently-destructive imaging workflow. You have to use layers because otherwise Photoshop will change your source JPEG. You don't need to do that in Lightroom, because the entire Lightroom workflow is inherently nondestructive. It literally makes no sense to attempt to do the same workflow into Lightroom 1:1. A workflow based on opacity of layers is not transferable to Lightroom.
The "curves" function is critical to me as I do a lot of black & white. That function in Lightroom seems very constrained and inflexible. I almost always use an S shaped curve in Photoshop derived from two very critically placed points. I just cannot do what in need to do with the LR "tonal curve" function.
An S-shaped curve is essentially just a finely-adapted brightness and contrast adjustment, as long as you don't do any reversals. The tonal curve in Lightroom will allow you to do just that. The only quirk vis-a-vis the Photoshop equivalent is that you don't modify the curve by "placing points", but by dragging the curve itself. This tool works only up and down, not horizontally, but this is not a problem because if you want to move the curve "right", you just grab it in a point to the right and drag that part up or down.
You can adjust the rate by which these control point adjustments affect the curve based on the image content - if you have an image that need fine adjustments in the darker areas, you just drag the "dark" part of the adjustment slider to the right, and then when you drag a control point on the curve you'll see that the curve becomes more responsive in the dark parts.
Exporting can be done using export presets. These work differently from Photoshop, but are very straightforward in themselves. Make a preset for each of your export formats and then that's it.
Honestly, I think it's just a matter of getting to know a few critical tools in Lightroom - the histogram adjustment sliders for the initial placement of the histogram, then the tonal curve tool which does the same as Photoshop's curves (except that you need to click in different ways to move the curve), and then the export tools. This is basically it. Your 10+ years experience in what buttons to click in Photoshop is not worth very much in a different program with a different logic. However, the underlying 10+ years experience what adjustments an image needs to look good is very transferable. It's just a matter of learning a new tool to make these adjustments, and the new tool (I find) is actually very straightforward in itself if you don't attempt to cram Photoshop button-clicking logic into it.