I want to write a hit counter script to keep track of hits on images on a website and the originating IPs. Impressions are upwards of hundreds of thousands per day, so the counters will be incremented many times a second. 
I'm looking for a simple, self-hosted method (php, python scripts, etc.). I was thinking of using MySQL to keep track of this, but I'm guessing there's a more efficient way. What are good methods of keeping counters?
If accuracy is important, you can do it slightly slower with MySql... create a HEAP / Memory table to store your counter values. These a in-memory tables that are blazingly fast. You can write the data into a normal table at intervals. 
Based on the app engine ideas, you could use memcache as a temporary store for your counter. Incrementing a memcache counter is faster than using the MySql heap tables (I think). Once every five or ten seconds, you could read the memcache counter and write that number into your DB.
How to write an efficient hit counter for websites