your kidding right? Do you really thing a microsoft product could handle a huge social network site? Please, a microsoft operating system and database like sql would drag to a crawl. Out of the top websites world wide, only a few like MSN and Hotmail are running a microsoft / sql site - everyone else is using Unix, Linux and mysql or a version of mysql. If its good enough for google, it should be good enough for you.
Kev, What does mySQL have to do with Microsoft? I think you are confusing mySQL with MSSQL. Then you go onto tell people that Google and various top sites use mySQL. Are you kidding? Before polluting the waters with your biased replies, do a proper research. mySQL can not support an exterprise level/amount data successfully UNLESS it is heavily modified. Oracle, DB/2 or maybe MSSQL (which you put down) would be the actual alternatives.
It really depends on how your application uses the database, how big your database is going to get, and how much reliability / data security you need. In the terms of large-scale enterprise applications, I have to agree with falsealarm. It can be made to handle a large amount of data and a large load, but it is not something that can be done without good hardware, and very good database and application structure. If you need to go down the enterprise route, you would typically put the database on a dedicated cluster with redundant load balancers. The problem you end up running into is the cost of hardware gets really expensive. But, it's still cheaper than going the Oracle / DB2 / MSSQL route. You also have to properly tune the database parameters, and you need to make a solid and efficient application. In my opinion it is possible, but if you do need an enterprise level database it is not something as simple as installing mysql on a computer and calling it a day.
Yes certainly reliable. But you need to less use searching in mysql. Facebook not only use mysql also many programming tools. I recommend use memcache at seperate server. It does ot quite performance on 1 server.
I guess I was not able to clarify my point as much as I thought. I first of all doubt Facebook is using mySQL. Even if they are, it is not a standard compile of mySQL and is heavily customized after which point it is no longer the same mySQL which is available to you and I. We should stop saying x and y uses mySQL, so it is reliable.