Have you upgraded to OS X 10.7 Lion today and there were absolutely no problems? If yes, you are either very lucky, actually not using any application which depends on properly loaded kext's (like truecrypt or cisco's VPN client) or you don't rely on GPGMail or Parallels Desktop. That's not everything by the way: PowerPC applications are no longer supported, there is no Rosetta anymore. Some companies like Avid for example do not recommend an upgrade right now. But since I'm not that much into music production, here are my personal experiences:
Truecrypt: As expected, Truecrypt 7.0a doesn't work after upgrading but Philipp Schmid's solution works just perfect. Given you encrypted a whole partition, you'll notice that your disk has been repartitioned by Lion's installer. It gained a an additional "Apple_Boot Recovery HD" slice and that's why.
GPGMail: Mail.app automatically deactivated GPGMail. GPGMail is currently not compatible with Mail.app 5.0 (OS X 10.7 Lion).
- Update (28th of August 2011): A few days ago an alpha version of GPGMail v2.0a3 has been released and - according to some comments - seems to work fine.
- Update (29th of October 2011): You may now also use version 2.0a4.
Tunnelblick: The recent stable version 3.1.7 is not longer working with OS X 10.7 Lion, you will need to upgrade (a reboot isn't necessary) to v3.2beta26.
Cisco VPN: You will be greeted with a nice "Error 51: unable to communicate with the VPN subsystem" which probably means that your kernel extension wasn't properly loaded. You don't need to try to reinstall, v4.9.01.0180 for Snow Leopard doesn't work anymore. There is a more recent v4.9.01.0280 available at cisco.com (release notes) but since I'm not really forced to use that particular client and Cisco's AnyConnect VPN Client works like charm, that's untested and I'm happy to drop another proprietary piece of software.
Parallels Desktop: As expected Parallels v5 (build 5.0.9376) also doesn't work (Parallels driver couldn't be loaded). Parallels will probably not update their Parallels Desktop v5, but they were kind enough to sent a mail yesterday, stating that their latest Parallels Desktop for Mac v6 (build 6.0.12094) is compatible out of the box.
Besides those third party applications, software update will automatically pull in Remote Desktop Admin Update v3.5, iWork Update 6 v9.1 and iTunes v10.4. If there is an application which depends on Java, you will probably be asked to install Java for OS X Lion. You may also manually download (DL1421) and install it. If you're working with Apple's Server Admin Tools, you're forced to upgrade since your old Snow Leopard Server Admin Tools have been automatically removed during upgrade. On first sight Server Admin Tools 10.7 (DL1419) are also working with 10.6.X Servers.
So you should really have a look at applications you rely on and check their compatibility before upgrading. It's definitely not the worst choice to wait until the first minor Lion upgrade.