I would definitely encourage you to find something else to process your searches. The similar_text function is night and day slower than using the database to search with. Even Regex Like in MySQL is faster and that's pretty sad. The problem with using similar_text is...
1. You need to load all data you want into PHP (that means you have HUGE memory overhead)
2. It only accepts strings, which means you're forced to throw it into a loop of some sort.
3. It only returns a percentage value, which means you need to either store another array or replace the key for each array item that you're searching through.
4. Once it's all said and done, you have to sort the array, then pop off the number of items you want.
That's dirty. If you ever have to search for anything over say... 100 rows you'll be paying for it horribly, especially if there are a lot of people that are using that search functionality.
Use Lucene. It takes more setup but its far better than any other options out there and once you've set it up once, you know how to set it up way faster the next time. FULLTEXT is easy, but primitive and has significant downfalls, especially if you have a small indexible database or your indexed content has a lot of the same content.
I personally dislike FULL TEXT, the reason for that is because your keyword must be at least 4 keys long.
This gave me problems when a user wanted to find my PHP IRC BOT tutorial and went searching only with "IRC". And people wont keep searching until they found the correct keyword.
The remedy for this problems was lowering the minimal keyword size in the mysql boot config (while starting it from cli), but that must be done as a server admin. So people on shared webhosts arent able to do that themself.
__________________ Nunchaku! Who doesn't like martial arts? =)
Like I said, there are some significant draw backs. The index must have 3 or more words in the index entry, all words containing 4 or more characters (by default). If you have high word saturation (like my company had an issue with "Orlando" in a project), FULLTEXT will ignore it until there is less total saturation of that word.