This appears to be the same as the iPad download location, noting that the 3.1.2 & 3.1.3 firmwares are the same as 3.2 & 4.0 when it comes to Installous.
All of the downloaded IPA’s land here :
If you have OpenSSH installed on it, you can easily SCP those files off your iPad and put them into iTunes ¦ so I hear 😉
Also, I found that with a simple:
find . -name Downloads -print