I've been using Pinboard for bookmarks since before browsers started offering sync. I can create and search those bookmarks in any browser, and since I use multiple browsers on multile machines, that's handy. My webmail is also accessible from any browser.
Syncing extensions and browsing history is not something I feel I need.
Pinboard seems to be minimally maintained. I've tried contacting the developer (it is just one guy) and have had no response. A bit concerning, if you ask me.
I have seen him being very responsive to paying customers and his charges are reasonable. However, it seems he did get deluged with delicious users whining at him after he saved that service, and you wouldn't reasonably expect a one-man business to be able to handle that.
You could always try tweeting him. He's also on HN.
Syncing extensions and browsing history is not something I feel I need.