As new sites and applications appear on a near-daily basis (think I'm kidding? Put TechCrunch in your RSS feed and see how many posts a day they crank out), you'll inevitably get shut out of sites with beta invites.
And with only so many friends in the social media space, what's a desperate beta tester to do? Until now, it was beg, plead and work your social networks. But there's a site that's got an answer.
Over at InviteShare, you can do just that - share your beta invitations with others, or ask for beta invitations from them. For example, when you sign up for GrandCentral, you get 10 beta invites. Maybe you've only given invitations to 4 people in your network - you can let people at InviteShare know that you have 6 invitations left. Similarly, you can put in requests for those hard-to-find beta site invitations, like Yahoo Mash, the aforementioned GrandCentral, Pownce, etc.
Now, don't expect the ultra-exclusive sites like aSmallWorld or Diamond Lounge to have any invitations there. Some social networks are too good for that.