Calibre is now THE center of my eBook 'experience' on my PC.
I download my books (95% of the books I read are free online!) online, enter them using Calibre, send them to my jailbroken iPad using WinSCP and wham!
Best reading experience ever!
I do need to clean up the author sorting a bit, since different books have different variants of the same author's name (e.g. Hayek F. or Hayek F.A.) but that will be a one-time big job.
I think the only thing I am left wanting from Calibre:
1) binary zip/rar download! I know a few users have requested this (as have I). I run Calibre and all my other apps in a custom 'sandbox' and your installer fails to install 100% of the time. (I get the error "installation directory must be on a local hard drive").
I know there's portable apps, but it's more a hassle than getting it directly from your site + user would have to wait for your wonderful updates.
I guess it would make it so much easier for a (minority?) few of your users to give us the option of RAR/ZIP file on your website, alongside the installer. Most devs do this and make the steps for people like me easier. If it's very time consuming, just let me know and I'll stop nagging
2) Calibre to add an option to mow my lawn.