Hey so I've been noticing lately that when I work on an image in Lightroom3 and then open it in Photoshop CS4, it's much darker. I open them in PS as sRGB and I have my colour settings as 'Web/Internet', so they should match, no?
Are you referring to raw files in each application ? If so, then it could be that Lr is using a more recent process than your Ps CS4 is using. It was upgraded in 2010. I can't say for sure what impact this has but in Lr you have the option of using the older 2003 process.
When you export from LR to PS, you should also see a dialogue box that asks you if you want to let LR process the RAW or CS4, and in your case I'd pick LR.
You may have clicked some "don't ask me again" button some time ago...
Yes I remember it saying something about not being able to process the RAW because a plugin was missing, but that only happened recently when I upgraded my LR and the RAW update didn't have any additional support for 5Dmk2 files, so I figured I didn't have to worry about that. Is there a way of getting that dialogue box back?
Assuming you have set up LR3 with CS4 as an "external editor":
Go to your raw file in LR, right click on the thumb, select edit, then edit in CS4 and the pop-up should appear, select render in LR. If the pop up does not appear, in LR on the very top right menu select Edit, Preferenses, on the General tab at the bottom click on Reset all warning dialogs.