While tying all these services together can save you a great deal of time, not every message is right for sending to all three services at once. Remember that Facebook, Twitter, and LinkedIn are all very different sites that users come to for very different purposes. A message meant for your fans on Facebook might not read as well on Twitter, or vice-versa.
Ping lets you create sub-groups, which you can use, for instance, to send updates exclusively to Twitter and LinkedIn only. In Ping, just select Create Group, then select a name for your group. Ping will then let you select which social networks you want that group to post to, and create the group. Once it's been created, just select your new group from the dropdown menu to post only to those services.
In general, however, you'll want to use services like Ping for messages that inform a broad audience of something of broad appeal, such as a product launch.
If you're trying to start a conversation, however, this approach less ideal. To solicit comments from your fans and followers, tailor unique messages to each social network. Otherwise it's tricky to match the tone of Facebook messages, tweets, and LinkedIn updates all at once while saying something interesting. Even if you manage it, some users will still resent the mass-broadcast approach if they catch on. Still, as long as you use tie your accounts together wisely and don't overuse it, it can be a great time-saving tool in your social media aresenal.