The concept is to enable sharing of virtual machines with anyone --- you can just log in, click on a server to share and your customer will immediately receive an email with a link that launches a Unix or Windows box on a timed lease. Easy.
Vendor can use this technology to give out demos, evaluations and POCs to their customers. Trainers can use it to issue pre-built training servers to all students in their classroom. The biggest benefit is cost: Amazon EC2 machines can lease for as low as 2 cents/hr, which makes this concept of VM sharing very attractive, even for small businesses.
You'll need your EC2 accounts to register: http://LabSlice.com/Register. If you don't have EC2 then you can sign-up (Amazon's new deal actually gives Micro-sized machines for free for one year if you sign up this week!) and then come back to the website ;-). Or you could just go to the contact page, tell me you're from YC, and I will add you onto my test lab account.
Thanks in advance for feedback, Simon @ LabSlice.