1) Even with hard drive prices inflated today, we're at over 9GB/$1 for storage. That means for $1 you can store 1.25 billion 64-bit integers. From that perspective, there is very little data (at least in terms of traditional RDBMS data) that is actually cost effective to throw out. To the extent that you do need to throw it out, you can wait until all transactions involving the data have long since completed.

2) I think you misunderstood what was meant here. His point was that your limiting factor really becomes throughput if you have the right architecture.

3) Indexes and cache locality also tend not to play well together. ;-)