I for one have experienced connectivity problems with my iPhone 3G over WiFi. My signal is never as strong as it used 
to be and even in the house I get no connection where I used to get a connection, all this after the 3.0 update.
Hundreds of people have been complaining of these issues of the iDevice not connecting to WiFi, less signal strength or saying you have a WiFi connection when you don’t.
Apple if fully aware of the problem and will be working to fix it. Some people think that the 3.1 update will fix these issues but some people don’t agree with this so we will have to see. If anyone is using 3.1 Beta do you experience any of the WiFi problems?
Some people have came up with many solutions to try and fix this problem, but they don’t work, some people even tried putting there iDevice in the freezer.
Sam's Blog 
I recently purchased a refurbished iPod touch 2g. I downloaded and installed 3.0, which generally appears to be working OK. However, when I downloaded Skype for iPhone/iPod Touch from the Skype website, no Skype icon appeared on the home page. Any comments?
Try re-downloading it from the App Store or go to the Spotlight search and type in Skype. If it doesn’t appear then it’s not been installed correctly and try re-installing it via the App Store.