The answer for us was “yes”, although there’s a lot more to it than that. I just wrote about doing this on AusGamers for a table that was causing us a lot of grief with really slow DELETEs due to the huge volume of data in there.
I found that gzip’ing the content before putting it into the database made a massive difference to performance – queries that would usually take minutes to run because they were removing up to gigabytes of data suddenly were dealing with 10x less bytes, which made a huge impact to the execution time.
The results were obvious – you can see in the graphs below the impact that was made.
This change might not be useful in all circumstances – obviously at some point the CPU overhead of gzip’ing might cause more problems than its worth, or something. But if you’re dealing with multi-megabyte chunks of text that MySQL only needs to pull in and out (ie, you don’t need to sort by the contents or do anything else with that data from within MySQL), it’s probably worth trying.