twitter, scaling and Amdahl's Law
a related post had a striking quote:
...the final point of contention in any traditional web application architecture, is the database. Get rid of that and you're home free.
wow. databases are the problem? maybe. serializing data from thousands of users into a single database can produce problems. but i think this is not a 'database' issue - but a 'storage' issue. replace database with file system and i think it still holds true.