Jeff,
I don't see it as a problem right now at all. As of now, the entire LVPC (Main site, forum, gallery) is taking up about 0.0086% of the server space allocated for the site. I'd obviously encourage people to link instead of using attachments (you can't directly upload/paste in a forum post), and I have built in limits on attachment sizes. I also have the ability to clean up and purge the forums.. for example, I can "purge" all threads that haven't been posted in in over 30, 60, or 90 days. I can select all or only specific forums to do this on and I can have it ignore stickied topics - ie, Stickied topics won't be purged. So I have alot of tools for keeping things in check. So if you post something really necessary, I would make it a 'sticky' so it won't get purged. But I'm pretty selective on purging and error on the side of keeping things.
The Gallery I will keep the items posted there for awhile. If I see things starting to pile up, I'll just delete all photos except the winner in that particular album.
If the image is posted on the net at flickr or any other site, I'd ask that they be linked to. However, if someone doesn't have access to a site right off hand, I don't mind if they use the attachment function as I mentioned, there are built in size limits that I already have set in there.