- Mobile equivalents of del.icio.us, sites where you can create your own personal directory or tag cloud of links. These sites usually default to links being public, viewable by anyone, although most let you mark some or all of your links as private.
- Sites that use a voting mechanism. These are the mobile equivalent of Digg.com. Links on these sites are always public and users can vote for sites they like or against ones they dislike and can also leave comments.
Pinboard
Usability: 
m.pinboard.in (xhtml-mp)
Pinboard is a good and mobile-friendly bookmarking service. The site is clean and simple and saving bookmarks is fast. The full Pinboard site at pinboard.in works great in the Android browser and with Opera Mini and Mobile and there's a lighter weight mobile version at m.pinboard.in.
Pinboard's features mirror those of the once popular Delicious.com bookmarking site before it was aquired by AVOS Systems and redesigned. Bookmarks include URL, title, tags and descriptions and can be public or private. Anyone, Pinboard member or not, can search public bookmarks or browse pages of recent and popular ones. You can share yours at m.pinboard.in/u:username. To share a single tag use m.pinboard.in/u:username/t:tag
Unlike Delicious, Pinboard is not free. There's a one time sign up fee, currently $10.09. The price is determined by the number of users times $.0001. That's an interesting pricing model. I can grok early adopters getting a better price. On the other hand the every increasing cost to join would seem to discourage growth - or maybe that's the idea.
I created a mobile-optimized Pinboard bookmarklet. You can find and instructions for using it here. It works with all browsers that support bookmarklets including Opera Mini, Opera Mobile, the Android 2.2 and latter browser, Safari, the WebOS browser, the Symbian Browser since S60 3rd ed. FP2, Firefox Mobile and Mobile Internet Explorer 9 and earlier.
Screenshots
Instapaper
Usability: www.instapaper.com/ (HTML5)
Delicious
Usability: delicious.com (HTML5)
Social bookmarking site delicious.com uses a responsive design that adapts to different viewport widths on mobile and PCs. It works very well with smartphone browsers and with proxy browsers like Opera Mini, UCWEB and the Nokia S40 browser.
Notesi
Usability: www.notesi.com/mobileonlinebookm... (xhtml-mp)
A free service providing secure, private, cloud based storage for your browser bookmarks. Notesi makes your bookmarks available in all your browsers on all your devices.
PhoneFavs
Usability: phonefavs.com/ (xhtml-mp)
PhoneFavs wants to be your mobile web home page. The site combines a mobile portal, a search form for all the major search engines, a social bookmarking service, a web to mobile transcoder and a mobile software store. None of the pieces breaks any new ground but together they provide a useful starting point for exploring the mobile web and creating your own custom web portal.
To get started there is a directory of around 300 well chosen mobile web site links. You can browse the directory, trying out sites. When you find one you like, you can add it to your personal My Favs directory by clicking the "My" icon that appears next to each listing in the directory. PhoneFavs can also import bookmarks from del.icio.us, Firefox or Internet Explorer.
You can also add sites from your PC web browser using a bookmarklet. Some mobile browsers support bookmarklets as well, including Opera Mobile and Mini, Mobile Internet Explorer and the iPhone's Safari. I've added the PhoneFaves bookmarklet to the Yeswap Opera Mini Bookmarklets page. Visit o.yeswap.com to add the PhoneFavs bookmarklet to your browser.
31-Dec-2014: Phonefavs no longer offers a mobile bookmarking service.
