I was hired to do some training for a photographer who was just breaking into the world of pro-shooting and digital photography that was using PSE4.
My opinions on the app can be summed up in one word:
I'm very familiar with PS/PSE2 and quite adaptable to editing software. PSE4 was like a mix of a slimmed down PSE2 and Google's Picasa program. You can read a review of PSE3
at DPReview and see what the interface is all about. You can turn that junk off though and get a program that is very similar to the full PS and you can find plugins
to give PSE curves and channel mixer tools.
PSE4 comes with a image browser/manager which used to be Photoshop Album. I loathe that POS. Again, you can learn more at that DPReview review.
To be frank, you may never even need the full power of
Photoshop. PSE and Lightroom can make for powerful allies.
As to using LR full time, I know Michael is and I am on the verge of doing so. I've transfered allot of images there (professionally taken and not). Depending on how the Beta 3 stacks up, I just might make the plunge fully.
PWP is Windows only and Seb is Mac.