Interesting question indeed. I have a similar post-networking event strategy but must be less popular since I haven't hit any sort of limit, but I asked Duncan Work over at LinkedIn about the entire issue and here's what he shared:

Dave, here's an explanation of LinkedIn's policies regarding invitation limits for those who haven't seen them before.

Because of complaints from members who were receiving multiple invitations from people they didn't know we now have a default limit of 3000 invitations that a member can send. Before the limit we had a couple of thousand users who regularly sent thousands – or even tens of thousands of invitations – with very low acceptance rates and lots of abuse reports. The limits have helped stop most of that -- but not all.

When you get close to the limit and send new invitations you'll see a message on the site telling you that you're close and that you can request more.

The best way to request an increase is to login to your LinkedIn account and use the Contact Customer Service form on our site.

As with all inquiries to customer service, they give fastest turnaround to paying customers and using the form above will get the quickest response. If you're not a premium account holder your request will still get answered but it could take 2 to 3 days, depending on how busy customer service is.

If the positive feedback from the people you've recently invited is high you'll get an increase of 500 additional invitations; and you can request additional invitations 30 days after your limit was last increased.

The threshold we use for giving a full increase is first, that the member's recent invitations resulted in acceptance rates that are at least average compared to the norms for LinkedIn members who have sent several hundred or more invitations; and second, that the complaints and abuse reports they've received must also be low compared to the norm. For people who are regularly inviting people who know them or who are inviting self-declared "open-connectors" (people who are open to connecting to most LinkedIn members) this isn't a particularly difficult threshold to get above.

If the positive feedback from the people you've invited since your last increase (or recently if a first-time increase) is below the threshold for getting a full increase of 500, you will initially get at least some additional invitations, often 100, so that you can establish a positive feedback score needed to get higher increases. People who repeatedly get below average positive feedback scores may not receive any additional invitations and will then have to wait a longer period before requesting more.

You can insure that your acceptance rates stay high by only sending invitations to people who know you, or to people who have indicated that they're open to invitations coming from people they don't know. Instead of using invitations to reach out to new people or others
you've had little interaction with, we suggest using InMails, OpenLink messages and Introduction Proposals for LinkedIn members. And in general we recommend finding other ways to get to know better the people you want to meet before inviting them to connect.

Of course, whenever there are limits, some people will try to get around them. For example a few have tried to get good feedback scores by sending a small number of invitations in a month and following the rules for whom to send them to. Then they hope that they can store
up large increases and send them all at once to whomever they want, not caring so much about getting a full increase the next time. We've had to make our rules a tiny bit more complex to prevent these kinds of games, but those rules affect really only a handful of people.

No rules are perfect. But by using feedback from the people whom users themselves choose to invite, and by regularly giving increases to people who consistently get good feedback, the system seems to be working fairly well.

Thanks for the inside scoop, Duncan. Please note that this material original arose on the My LinkedIn Power Forum discussion group too.