Sending tabs and syncing bookmarks is especially useful. Find sth. nice to read on the PC but have to leave, send the tab(s) to your phone. Stupid registration form, bad mobile site, sth. to copy or paste from: send it to your laptop.

Also, a bit off topic, but the Tab Queue thing in Firefox for Android is incredibly awesome. I have some newsletters that I follow, hit the links, they're queued in Firefox, and I stay in my (K-9) mail app. When I've gonr through all the newsletters, I switch to FF, and all my pages are there.