A
JV giveaway event is a site created by online marketers who agree to utilize their lists of subscribers to help build the mailing lists of all the members involved. By taking part in such an event each participant is likely to build up their own subscriber list by taking advantage of the combined power of all the other list builders who are taking part.
The way it works is every single participant of the JV giveaway register one or more free products along with their squeeze pages that they will utilize to collect new sign-ups. They then agree to email their opt-in list on launch day promoting the giveaway event and all the gifts contributed by other members.
Are JV giveaway events really a good way to construct my list fast? The answer to this question is: it depends on the situation. If you are running your own JV giveaway event than it most certainly is.
Even if you are unpracticed and the event is not so well run, you will build your mailing list by 100's if not 1000's of subscribers. Effective events may add to your list many 1000's of new subscribers but you will have to really be awesome at it and have a reputation that attracts people. You will benefit greatly if you could find yourself a seasoned partner to manage the event together.If you are registering with someone else to giveaway as a contributor than you will boost your subscriber list.
Will it be a huge growth? Again - it depends on the situation. If this is a well known event (running at the same time of the year for several years) and if you do great work with your contribution (more on that later) then you can see 100's of new subscribers on your list. However, most of the JV giveaway events I've seen are either conducted by unacquainted people or are run by "professional" event creators on behalf of others. As luck would have it, most of those are not so well run and the results for contributors are way worse than one could hope for.
Conclusion
JV giveaway events are one way of developing your list. Use them well and you will benefit.
Use other ways to build your list as well; don't rely on JV giveaways alone.