My Wiki has been mysterious getting slower and slow and I didn't have a clue why. Today I happened to check the log file's size, it was over 10m. So I removed it and the Wiki was back to normal. Conclusion: you have to have a way to manage the size of rails applications. Some people just turn off logging altogether. I opted to set the log level to error. Another option would be to have a cron job remove the file periodically.
Update: Not so sure the large log file was the cause anymore. I still don't know what caused it, may a memory leak of some sort, or maybe this is just the woes of using a shared host. The problem hasn't come back so far, so I haven't been able to look further.