Do You Need Photo Editing Software?

Probably not, short answer ;)
long answer
I really think for many if not most, the editor that came with their camera will be enough..especially if you are the type that sometimes just downloads straight from the camera, maybe crops and makes prints or emails to Grandma.
But say you want to be more creative? I have and use a bunch of different programs but the one I think would be most usable for the majority of basic camera users is Photoshop Elements. I have 5, 6 is out, not sure how much it's changed.... It has most of the features of the full version ($$$$$) Photoshop but at around $80 won't break the bank. It allows you to do the basic crop, clone out the odd person's stray head* that you didn't notice, adjust exposure, saturation etc. I do think it has a learning curve, just like most everything in life, but if you want to get a little fancy with some of your photos it is a good buy. Some like Corel photo pro( think that is the right name) but it is not as user friendly to me but if you are in the market for a bigger badder editing software than what came with your camera , down load the free trials both offer and see which makes things easier for you. They are about the same cost.
If you have a dslr and would like to start shooting in raw, you can still come out ahead in the wallet if you get elements and Lightroom...the Beta addition that is out now( new release due in June) is great. I love it for converting raw files...but if you don't shoot in raw it's worthless to you. Elements can be used with a raw processor via the free download of Camera Raw by Adobe that is pretty much the same as the present Lightroom but not as good as the new edition( unless they update Camera Raw as well). You don't really have a lot of batch processing though and since you have to process raw files, that can be a pain if you just want family snaps.
If you are a relatively dslr newbie, maybe we'll talk about Raw vs Jpg, next blog so you can see what you have been missing.
* they could be really odd and sensitve about getting their photo taken if they have a stray head so cross over to the other side of the street and don't take their photo...but if someone sticks their head in your photo at the last second, use the clone tool to clone that out.