I totally agree with this. This practice seems like it's sloppy programming. Plus, you have to remember to log out of certain sites or else if somebody steals your phone, they have access to the data...of course, most secure sites will log you out after x time. But still. If you're in a hurry, I like to kill the apps. No can do with Android, it seems.
I've also noticed that some apps cannot be closed at all. Like Seesmic - how do you kill that thing? I cannot even DELETE/uninstall it. Any ideas?
Absolutely...programs need to QUIT when exiting. People can say that you can run 100 apps in the background, but the point is that each running app is taking SOME amount of resources. Yes, the Linux kernel is good at multitasking and threading, but resources are not unlimited on this phone. Once you hit a limit, you will notice a performance degradation. Like if I run Homerun Battle 3D (really awesome 3D game by the way) and I go to the home screen with the game still running, you can tell that the phone is MUCH slower. Yes, it's relegated to the background, but it's still using resources! Also, I've seen my phone get slow when all these programs autostart (corporate calendar, facebook, market, browser, maps, etc.).
What really needs to occur is there needs to be a way to disable services\apps from starting on their own (at least without rooting). I don't need Corporate Calendar to run in the background; why should I be forced to run it?
If someone uses a task killer and claims it slows down their phone, they're using it incorrectly. Think about it, how could killing a program and regaining resources make a phone slow down? Maybe if you use a really crappy app that has memory leaks this could happen, but it has never happened to me with ATK. But like anything, using a task killer is a personal preference; some people like it, some people don't. At least we have a choice...
Oh, uninstalling
Seesmic...if you can't remove it with Settings > Applications > Manage Applications, you could try to download an app management tool (like AppControl from the Market). In there you can long-press an app and remove it that way.