I started using Thunderbird several months ago but it didn't work out. There were lots of features missing (mark all as read, OPML built-in, read new feeds at one place to name a few) so I had to come back to SharpReader, a fine product. I found Thunderbird slow, less-featured and not very interactive, something you normally don't expect from a mozilla product.
For those looking for Thunderbird OPML extension, I've used it, it works well for OPML import/export.
Improved Thunderbird PML
Another hack: To read new feeds at one place, I had to create a search folder with selected criteria to look into my subscriptions and bring the newest post; something avaialble by design in sharpreader.