I have been using a Sprint Overdrive for a couple of weeks as part of my Sprint 4G series and have indeed found some issues with the connection between it and the iPad. In what may be some of the most comprehensive connectivity testing with the iPad to date my Mobile Tech Roundup podcast co-host, James Kendrick, posted on possible ways to minimize WiFi issues with the iPad with some discussion of the Overdrive. By default, the Sprint Overdrive uses 64-bit WEP encryption for security on the Wi-Fi network and that is what I continued to use. With the advanced settings of the Overdrive you can change that to other security methods and James recommends and finds WPA2 to be more reliable.
James also tested out his connection at home so check out his thoughts on this. I personally have an open connection at home since my house is too far from any neighbors to worry about anyone jumping on my connection and being at the end of the street means you have to park in my driveway to use my connection, which cannot happen without me coming out to chat with you and see what you are doing. I haven't had any connection issues on my open WiFi 802.11 b/g connection.