ebay is always changing the rules about links, so be sure to refer to it fairly regularly.
(btw, ebay considers text such as 'yoursite.com' to be a link, even though it's not clickable. same with images that have .com in them that arent clickable)
That being said, their policy about links in listings is at http://pages.ebay.com/help/policies/listing-links.html
Currently, the policy on listings is:
One link to a page that further describes the item being sold in that listing. This outside of ebay page cannot contain other items for sale outside of ebay, but CAN have links to other items for sale outside of ebay.
One link to your email address that opens an email client for potential buyers to ask questions about the item in that listing
Links to photos of the item for sale. This gallery page may also contain discrete links to other pages that offer items for sale outside-of -Bay, but may not contain descriptions of or links to individual items on other sites.
Links to your eBay (including your eBay Store) or Half.com listings
Warning - this is where people often get in trouble for keyword spamming, by having links such as ones that say "view my earrings" in a listing for pendants, etc. if you do links like that, do the words as an image rather than text.
Links to your About Me page (in addition to the About Me icon already provided by eBay)
Links to your “Add to My Favorite Sellers and Stores” page
Links that provide credits to third parties (see various restrictions)
One link to your listing terms and conditions (providing that the most relevant information is within the listing itself and this page may not include any links to Web pages outside–of-eBay)
About Me page - rules are at http://pages.ebay.com/help/policies/listing-aboutme.html
The About Me page may not promote outside-of-eBay sales or prohibited items, nor may it contain links to commercial Web sites where goods from multiple sellers are aggregated by a common search engine (ie: amazon.com).
You may link to your own Web store or Web site. However, you may not directly offer any non-eBay merchandise on the About Me page itself.
So, on Me page you can say "Visit my website" but cant say "get xxxxx from my website"
Stores policy
http://pages.ebay.com/help/specialtysites/stores-ov.html
Note: I couldnt find a links policy for custom store pages, so would assume that it's the same as links policy for listings (but dont know if that's the case or not).