Is it possible to use Time Machine via AirPort Disk without storing the backup in a sparse bundle? I've had bad experience with sparse bundles and would like to avoid them.
It's not been shown (yet) how to hack apart the Time Machine process on Lion sufficient to do what you ask (skip the sparse storage format).
I too was bitten by early network based sparse bundles. Since mid 10.6 (maybe 10.6.5) - I've been unable to break Time Capsule based despite repeated tests to be really mean. This includes pulling the power of the capsule in the middle of backups repeatedly to regain confidence. This isn't something I'd do on my main backup, but the Snow Leopard implementation is now rock solid in my eyes.
Realize that by having a less reliable network, this sparse format is actually more reliable overall and has checks and balances to make sure you get a good backup even when bad things happen.