everything you see is the amout of unconfirmed transactions at this second. No Graph over the time or something like that.
sorry, i think 'blockchain' was the wrong. i meant transaction - chain - if you can call it like that.
As provided above, there are 503 unconfirmed transactions (when I wrote this) (meaning they were announced on the network, but have not been placed in the block chain). You can see them all here: http://bitcoincharts.com/bitcoin/
If you wanted to know how old each of them are, you'd have to write a script. However, transactions age, as transactions age, their priority to be added to the block chain increases, until they are finally added. Transactions with a transaction fee have a higher priority to be added.
The oldest transaction currently waiting is 10 days old, but that's because one of the inputs (from) is unconfirmed, probably because this transaction originated from another unconfirmed transaction (which is true):
2011-06-06 14:41:16 c92b02348641084f82662f2a7f8d8840bc5421b1a1dfad1cdb52acc263ecd0a7
This is a low priority transaction.
This transaction includes 0.01000000 BTC as fee.
size: 224 bytes
input: 0.09000000 BTC
0.09000000 BTC from unconfirmed 2bcde2249216ef17b015f05fb05246add6b1fa06e5709dc86ba13c9938a6f64a:0 (1NEq1aCE4PVdWYzkjRqBPKm538FrvLpZb6)
output: 0.08000000 BTC
0.08000000 BTC to 1JwDpfZnKrw54pKJvV3SXiorLNSPVWPht