To spruce up the today screen & also to add a lot of functionality, look at Dashboard (snoopsoft.com).
To add functionality to your contacts, calendar, notes, & contacts look at Pocket Informant or Agenda Fusion (developerone.com). I favor Agenda Fusion, but they are both great apps and both have a lot of supporters.
Applications don't close when you hit the "x". To give you better control of applications and access to internal functions, look at Gigabar (free!). There are many more similar applications.
If you like calculators, look at
Jonathan Sachs Eval, or check out Calc98 (calculator.org). (Both free.)
Any PPC needs to be soft reset. If you're worried about punching a hole in the rubber that covers the soft reset button, try
Shutdown (Free!)
It's a big world out there -- plenty of fun things. I haven't heard of a PPC virus yet, although as more of them go online, I'm sure it's just a matter of time. I don't often disagree with advice posted on this forum, but almost all of the programs written for the Arm processor work fine on the Ax. There are a few exceptions, but generally they don't cause a lot of trouble. Most of the major apps that didn't run on the Ax have been upgraded, because of the great popularity of this device.
Relax. Enjoy.