Oy--lots to explore here, and I did at least a fair bit of looking around and applying.
I started out creating a start page in Yahoo--it's a site I already use for email, and I've never taken the time to personalize a start page before, so I did. Again, since I already use some Yahoo services, I did go ahead and make the start page I created my personal home page. Out of curiosity, I made an iGoogle page. iGoogle offered many similar options; I particualrly like some of the things it pulled in when I added a "Books" tab.
The online calendars are one I will definitely find professionally (as well as personally) useful. I created calendars on a couple of the recommended sites; the one I decided to settle on and will use is Google's. I liked the ease with which it can be shared; I entered my March meetings and library special events on a calendar and shared it with my colleague for her to enter hers. It will be useful for both of us to have an easily accessible view of our work events--and useful as well to be able to check it from home (so I don't schedule a dentist apointment at the same time I have an early meeting or something!).
I'm a list-maker, so the "Ta Da List" and "Remember the Milk" sites had a certain appeal (nice that you can check off tasks accomplished, too--that's always satisfying). The site may well be handy for keeping track of longer-term lists, but for short-term lists, I don't know how much handier it really is than my current list-on-the-back-of-junk-mail method.
Backpack looked like it had a number of useful services rolled into one. However, I did note that some of its services are by paid subscription--and truly, by the time I reached Backpacker, I was getting burned out on sites to keep track of/log into and check. While I read about it, I did not use any of the features.
As for recommended sites--PDF converters are certainly handy, and I liked that the PDF converter will also convert information FROM pdf to other (editable) document types (albeit with a 2 page limit for non-paying users). Zamzar was certainly also another site I took note of since I, too, have experienced the frustration of not being able to help someone open their document at the library because they're using a program either that we don't have or that simply isn't compatible.
I read through the information about other sites and tools, but it seemed like most of them had either been already covered in this or a previous thing, or they were a bit above me in terms of tech-savviness.