Support for WAS 5.0 will be withdrawn on September 30, 2006.
This has been previously announced a year ago, but now it's been announced again.
You can find dates like this on the IBM Software Support Lifecycle page, which I discussed in IBM Software Support Lifecycle and End of Support. I've also started documenting support stuff on my wiki under IBM Software Support.
So, if you're still using WAS 5.0, what should you do? Upgrade to WAS 5.1, 6.0, or 6.1. No end of service date has been announced for WAS 5.1 yet, so it's good at least another 12 months (September 2007 or later).