There are eBay ID's with digits only, just digits 0,1,2,3,4,5,6,7,8,9.... and no letters...

Is it good or bad?

I say not good and not bad, but I have found one defect in multiple-feedback link function:
At the SITE MAP of eBay (  http://pages.ebay.com/sitemap.html  )
you find the link called LEAVE FEEDBACK FOR A MEMBER (  http://feedback.ebay.com/ws/eBayISAPI.dll?LeaveFeedback2  )
When You enter there into the line of FIND A TRANSACTION the User ID which has digits only, the system does not find ID
and gives You the reply:
There is no match because:
* You have no transactions with 111222333
* Or the time limit for leaving Feedback (60 days) has expired.
You can try again with another User ID or item number.
As a result, the owner of the Digits-Only User ID receives less of feedbacks, than in average given by transaction partners.