When starting with the simple Apache web-server test profile, there is some fluctuation in the results for both 32-bit and 64-bit Ubuntu. The area where the performance changes the most is Ubuntu 9.10, which marks when the default file-system was changed from EXT3 to EXT4. Since the switch to EXT4, the performance has been improving modestly.
The PostgreSQL database server workload has also been more interesting since the switch to EXT4. The performance of PostgreSQL with EXT4 was at a high point in Ubuntu 10.04 LTS, but has settled down a bit as improvements were made to better ensure data integrity. With Ubuntu 11.10 there is a slight increase in performance. The 64-bit Ubuntu performance has also improved over 32-bit Ubuntu in the past year and a half.
The SQLite performance is also as expected for the file-system.