I used to use XMarks to sync bookmarks across browsers, but it didn't sync custom search engines and it didn't support all the browsers and OSes I used. superboyac convinced me to use Linkman for all my regular bookmarks (the free license through DonationCoder helped too), leaving only the custom searches that wouldn't sync. I looked for a service like yubnub.org that could be personalized, but never found one. My temporary solution became more and more useful so I decided to start making it into a real service.
It's called Shortmarks (Shortcuts + Bookmarks) and is aimed at someone using bookmark shortcuts and search engines on multiple browsers or machines. You set Shortmarks as the default search engine in your browser(s), then add your shortcuts/search engines in Shortmarks. You can then use those shortcuts from any browser that supports custom search engines (Firefox/IE/Chrome/Opera) on any machine/OS, and if you're not on one of your machines you can use the site directly. It authenticates against your Google Account (I plan to add more account types in the future) and comes with a default set of searches that you can customize once you're logged in.
You can use a single keyword for both a direct link and a search, so you if you typed 'gp' it would go to Google Maps, but if you typed 'gp los angeles, ca' it would perform a search for los angeles, ca on Google Maps. Another feature is the ability to search for one phrase on multiple sites. After typing the phrase in the field at the top of the page, hit "Update search queries" to puts the phrase into each search engine link, so you can open several in tabs. It just occurred to me as I was writing this that I could use FARR to launch Shortmarks searches too. I'll have to look into that.
Anyway, the site is: http://shortmarks.com/s.php and I've written up some basic instructions to add it to your browser (with screenshots from ScreenshotCaptor of course)
I feel that the main barrier is ease of use. If I were to set it up for someone, I think they would see its value, but it's not too easy to get started. My goal is to make it easy enough for less technical folks to use it without assistance.
It's still in development but I've been using it for a few months and I love not having to sync anymore, and being able to open any browser on any machine (even my iPod) and having all the same shortcuts and search engines.
I'm curious to hear feedback. If I'm the only one who finds it useful, I'd rather know that before I devote a lot of time to it.
Thanks in advance.