When you “upgrade” to Lion, be aware that Apple will silently wipe your “auto install / update” settings, and start aggressively downloading every update it can find for every Apple app you use.
In my case, this was gigabytes of data – I really don’t care (and don’t want) “upgrades” to PhotoBooth and other trash that Apple pre-installs. But, because Apple wants to force these on you, they’d already wasted large amounts of bandwidth (on my laptop – on a desktop broadband connection, I wouldn’t care), and reduced my internet browsing for a few days before I found this out.
So … when you upgrade … remember to open “Software Updater”, and change the setting (that Apple has overwritten), back to “don’t check automatically”. Sadly, there’s no setting for “don’t download stuff unless I tell you to” – but at least turning off the auto-check avoids this.