Is there any way to track an individual bitcoin (or satoshi)? For example, if I wanted to "collect" important bitcoins is there any way to track a coin rather than a series of transactions? If I wanted one of the bitcoins from the infamous "Bitcoin pizza" purchase, for example, is there any way to do so?

Perhaps the question I should be asking is more like "Do bitcoins themselves even exist or just the records of transactions?"
Here is a possible schema describing transactions from two addresses A and B that contain initially 50 BTC each:
     (A) 50 btc --tx1-----------------------&gt; 25 btc (C)
                   \
                    `-&gt; 25 btc (D) --.
                                      \
                                       tx3--&gt; 50 btc (*)
                                      /
                    .-&gt; 25 btc (E) --'
                   /
     (B) 50 btc --tx2-----------------------&gt; 25 btc (F)

There are three transactions here, and they mention only values: those transactions are stored in the block chain like:

tx1: (input on A: 50BTC; output on D: 25BTC, output on C: 25BTC)
tx2: (input on B: 50BTC; output on E: 25BTC, output on F: 25BTC)
tx3: (input on D: 25BTC,  input on E: 25BTC; output on *: 50BTC)

Only global amounts are involved, not individual satoshis. Could you tell where each of the satoshis in * came from? A or B? Just impossible.
Conclusion: There is no such thing as individual satoshis, they don't have identities in the Bitcoin framework.
(And it's the same, or even worse, for bitcoins. An individual bitcoin is not well defined. It might be a grouping of smaller amounts in the same place (wallet), or at the same address, or in the same transaction, but at a given point in time.)
It is however possible to track money flows between addresses, which may “dilute” into other flows, as illustrated in this answer.