Wow! I have been experimenting with calibre as a library management tool and feel like I have been reborn! I must admit that I've spent several hours digging through old posts on MR and reading through the user manual. I also have programming experience which probably helped in interpreting the template language faster than a total newbie would. I also have experience with calibre for metadata, conversions, Fetch News, and "Send to Device" for my Kindle. I really recommend reading through the help info on the calibre website and also looking at the keyboard shortcuts.
Here are some observations. I was not aware that the user had so much flexibility to set-up custom columns. It has allowed me to create custom columns for data such as Source (where I got the book), Read Date, Read (Yes or No) and genres. Having genres allows you to be creative in how you use Tags without creating a bazillion collections. I have created a hierarchical genre structure that shows up in the tag browser (very cool for organization!). I have loads of books that belong to series, and I feel like they are better organized now. I have installed several custom plug-ins that I didn't realize were available. I love the ability to Count Pages. And, there is a plug-in that retrieves metadata from Goodreads (yeah!).
I'm still deciding on the best way to organize my books, and I haven't imported my entire library into calibre yet. I've only transferred a handful of books onto my T1 while I experiment. However, here's an example of what I've got so far on my Collections screen. I thought it might help someone if they were trying to decide between the Sony Reader software and calibre. I created a custom column for genres and formatted it to my preference with dashes rather than periods. I have collections based on Read status and whether the book is tagged Fiction or Non-fiction. I also have collections created from Series information. I think I'm going to rename "Read Tags" to be "Status" and then those items will sort in my collections at the end of the list alphabetically after My Tags and Series. I am quite happy so far!