Especially when mass invitations are being sent out, please heed the information that these should be sent out from the LinkedIn platform, not via a mass regular email. This enables recipients to click on the LinkedIn acceptance button.

someone should post a "Best Ways to Send out LinkedIn Invites" to Post as a reference

Most of the original Lions actually don't know the best way to send invites since we haven't been able to send out invites in over 2 years

In the "old days" -- you just uploaded a csv file to your contacts, linkedin delete duplicates, and determined, by email, which are LinkedIn members already, and which one's you are and aren't connected to -- and then you just invited all of your contacts who are on LinkedIn but whom you aren't connected to (harder to explain this process than to just do it yourself)

The early toolbars tried to send the same sort of email invites by first screening your invites on the LinkedIn server to be sure you weren't already connect to them, etc but the LinkedIn server weren't reliable so a bunch of us ended up spamming both people we already connected to and to people who had no idea what LinkedIn was ...

I hear that many people use the current toolbar without problems -- it was certainly a good idea but just didn't work well originally -- I've not used the current version but apparently it is fixed so it may also be an option for some and even preferred by others ...