Are there physical Bitcoin? I have seen several folks selling "bitcoins" on Ebay and the like - but they are made of base metal and have no real connection with the bitcoin concept other than the symbol.

I'm wondering if some number of bitcoins could be permanently assigned to a coin (i'd plan on about 10 bitcoins impressed into a one ounce silver round).  I'm thinking of having a public registry of bitcoins assigned permanently to individual coins.  Said bitcoins could be reassigned only in the instance of the "surrender" of said silver round.

I appreciate the fact this reduces the portability of bitcoins, but it would be an interesting method of storing value.
There absolutely are. As a matter of fact, Casascius already offers a 10 BTC silver round in addition to his better-known 1 BTC brass coins and 25 BTC gold-plated brass coins. While not coins per se, the same principal allows for bitbills and other physical Bitcoins.