I've evaluated MySQL before, and have never considered it a good and viable product. I'd almost put it in the "it's more a theory than a true product" category. I'd put SQL Express '05 over MySQL.

We've been using MySQL for about a year- ever since we learned to our astonishment that it was running invisibly recording call billing stats on an Asterisk install on a 1.3Mhz PIII desktop with 256Mb ram running centos, webmin, sendmail, fetchmail, qmail, spam assassin, asterfax, voicemail, Meetme, dictation, conferencing and a whole host of other stuff. That's when we realized the resource gulf between Linux and the Windows world. We may think it doesn't matter to the sorts of customers we both serve, but Linux (with MySQL) is making a stealthy entry into many corporates (depending where you look, as much as 50% penetration by the end of this year) in the form of VOIP boxes.

If you want to check it out, visit www.trixbox.com and download a distro to install a pbx on one of those old desktops that aren't otherwise usable any more ;-) I've got one of those at home with direct dial-ins in the USA, UK and Switzerland running with an interactive menu, voicemail, menu-driven call forwarding to cellphones etc... I'm paying about $10 per month including 500 international calling minutes. You can use something like Skype for free but quality is variable and you don't get the physical landlines for people to ring, or the IVR.