I've switched to mac mini 2 months straight. People like us have some kind of weird affection to hardware. And mini is just so cute. Without any reasoning I've rushed to order a mac mini. From the day arrived I haven't turned on my Linux systems.
Here is a list of applications and tips.
Fugu - it is a WinSCP like application but a good wrapper around SSH, including ssh tunnels etc.
Adium - already mentioned a must have multi protocol IM
CocoaMySQL - A decent MySQL gui. But lookout for mysql 4 authentication hack.
VNC - Something I can't live without.
BluePhoneElite - An open source app for many bluetooth enabled phones. Manages sms, integrates with address book syncs calendars. A must must must have for me.
SubEthaEdit - A strangely good editor. Allows group editing if you have more mac users around (rendevous). But as an editor has the ability to understand syntax and create dropdown list for function headers, object definitions in a file. Fugu + SubEthaEdit is a very good combination.
Skype - name tells it all.
The one thing that mac mini lacks is microphone. I've managed to solve it by using my Logitech cam's built in mic. although iChat only uses firewire cams.
iEatBrainz - A musicbrainz client to correct you MP3 tags based on the fingerprint of MP3.
VoodooPadLite - A standalone application to create wiki like content. It helps me manage my mess, unorginized to do, some urls I'd like to take note of etc.
In your Applications/Utilities directory there is an application called keychain manager. It is a kind of a systemwide wallet. But the good thing is that you can use it to store your security account information. The good thing is that it can sit on your menu bar and you can lock/unlock any chain and access information easily. There may be many other alternatives but this is built in and easy to use. When I leave my desk for a lunch all I do is to "Lock all keychains" so that no appcalition can access any information even the system is turned on.
Disk Utility - Built in app in the Applications/Utilities folder. Let's you create dmg image files as well as burn CDs and DVDs. if you don't have a third party app like Roxio Toaster.
Hope this helps.