Like a few other folks, I decided to play with iiBench and see how fast I could insert 1B rows into an indexed InnoDB table. Mark Callaghan published an excellent writeup of the theoretical and practical limits when index size >> buffer pool... but I bent the rules a bit ;)
The platform I ran iiBench on has four dual-core Xeon 3.2Ghz, internal 10k RPM 8 disk RAID 10, and 128GB of RAM. That's a lot, I know, but it was built precisely to avoid InnoDB's performance drop when an index does not fit in memory. It took just 22 hours to run a single iiBench process and 10 hours to run four processes in parallel (each doing 250m rows)! This was achieved without modifications to the iiBench code, using standard MySQL 5.1.30 binaries, the following innodb configuration parameters:
innodb_buffer_pool=100G
innodb_max_dirty_pages_pct=50
innodb_support_xa=0
innodb_flush_log_at_trx_commit=1
innodb_flush_method=O_DIRECT
and binary logging enabled (had to purge master logs very frequently!).
Here's a graph of inserts/sec and CPU usage during the single-process test ...


... and during the multi-process test ...

