Don't what new purchasers to have to register or find out that they have forgotten their password after a year. One of my sites only sells tickets for an expo once a year so this is a problem.
Well it's now fixed by Burnbright.
Burnbright's new fork offers has this and more. Have a look at:
http://ss-shop.org/
or git
https://github.com/burnbright/silverstripe-shop