Is This A Common Problem?

The first 2 are at ISO 1600. The second 2 are 800. One of each has been lightened by +10 (+5 really) in Lightroom.

Something went wrong with the unbrightened ones

You're all excused. Now go get some new glasses.

I don't always conform to this for two reasons.

1] Often I like to fix one thing further down the slider list before fixing something else. Sometimes I like to fix expose before colour balance for example

2] Speed of lightroom itself. For example the sharpening and noise reduction are every CPU intensive, so I always apply these at the end. Not by choice, but becuase it can save a lot of brain ache and frustration on long editing sessions.

The advantage of Lightroom is that, unlike most other image editing programs it's editing is non-destructive, so there's no reason to perform edits in a particular order. i.e everything you make a new edit ALL edits are reapplied. This method is also more CPU intensive.

One of the questions from the Original Poster was about whether some settings would affect the RAW file. We've had a thread about this a while back when I first joined when I asked about applying chromatic abberation corrections in camera.

What I learned from all that and further experimenting, is that (as mentioned just above) settings that would be applied as 'processing parameters' to a JPEG will not affect the basic look or quality of the RAW file. This applies to settings such as : Noise reduction, Chromatic Abberation, Distortion Correction, Custom Image settings such as Saturation, Hue, Lanscape, Vibrant, sharpness etc etc. They would be applied to any outputted JPEG.

Be aware though, that even if not outputting JPEGs, having some of these settings activated will slow down the camera shooting speed - the processor carries out the calculations and stores the data in the RAW file.

This brings up the second point - all of these settings will be recorded in the RAW file. If this file is then opened in a program that can read and apply all of these settings, then you will see their affects on the preview when you open up the file. The only program I am aware of that can read and interpret all of these settings is Pentax Digital Camera Utility.

If the file is opened in another program, (eg Lightroom, Sagelight etc), you would not see the affect of many of these settings, just the standard preview of the base image.

I just wanted to point out something here - there is nothing unique about Lightroom in respect of its edits being non-destructive. This is simply the case because it acts (when using RAW files) as a 'Raw Converter', as opposed to a image editor (which Photoshop is). All RAW converter programs work 'non-destructively', that is the nature of the beast. The changes made to the sliders are just recorded as settings data, and applied through processing when requested by the user (such as ticking a preview box).

You can happily and non-destructively change settings back and forwards in any order in a RAW converter, and it will not affect the final output at all. You only commit to that output when 'Saving As' - to a Tiff or Jpeg. Most converters will store the settings you made as metadata, either written into the RAW file itself, or as seperate 'Side Car' files that will open when you reopen the RAW again, and return all the sliders to the same settings.

I've just caved and gone back to lightroom...

Picasa just doesn't the same kind of power... Photoshop has too much going on - and there's not much else in between of any worth...
I need to start shooting RAW again so it makes sense...

I did find a piece of open source software for those running Linux OS's that appears very similar to lightroom - 'Dark Table' I'm going to try it on my old laptop at some point...