Windows 7 Professional and DEP?

I've been running Windows 7 Professional (x64) for some time now, and one of the security features I only just recently learned about is Data Execution Prevention. I checked to see if DEP was enabled or not, and found that it must've set itself to "Turn on DEP for essential Windows programs and services only". I'm thinking about setting it to "Turn on DEP for all programs and services except those I select", but I'm concerned about system stability.

I've read that DEP can crash a great number of programs, and that it's typically unclear that DEP causes the crash at the time, leaving the user to wonder what happened. I know that exceptions can be made, but I'm worried, because I don't necessarily know every executable that each program uses in every situation. For example, I recently learned that Steam (which I use often!) has problems with DEP. Additionally, Steam updates itself automatically by spawning a program called SteamServiceTmp.exe, which it deletes after patching the main Steam executable. If SteamServiceTmp.exe causes a DEP problem, I doubt I'd realize it, particularly since the executable doesn't technically exist on the machine. If something similar happened for another program, I'd be way clueless about it. If it crashed my antivirus (NOD32 v4), I'd be in big trouble, too.

So, short story: How can I expect DEP to impact my system stability? Is it a good idea to turn it on? Is it a bad idea to turn it on after running for months in the "Turn on DEP for essential Windows programs and services only" mode? Thanks!

If your computer is frequently infected, you may want to have DEP monitor all programs. However, if you have an up-to-date antivirus software and software firewall and, preferably, are behind a router, the standard, pre-set configuration is probably fine. To learn more about DEP, see Data Execution Prevention: frequently asked questions

A word of caution, I understand that Steam users are frequent targets of phishers.

Try it.
If you have a lot of programs blocked by DEP then go for only Windows files.

In my case it's only one old game which doesn't support DEP so I excluded it, everything else under DEP

Usually when DEP blocks some application it gives massage via tray ballon saying DEP closed application so you will know.
But I have seen on some systems it not giving this warning

But read about it more and decide if you need it and try it.

Something like this: (it's XP)

My NOD v4 runs perfectly fine under DEP

jav said:

Try it.
If you have a lot of programs blocked by DEP then go for only Windows files.

In my case it's only one old game which doesn't support DEP so I excluded it, everything else under DEP

Usually when DEP blocks some application it gives massage via tray ballon saying DEP closed application so you will know.
But I have seen on some systems it not giving this warning

But read about it more and decide if you need it and try it.

Something like this: (it's XP)

I enabled this for all programs some time back and have only encountered one such popup. The popup did give the option of adding it to the list which I did and it worked. That was in XP. So far in Win 7, no alerts.

Fantastic. Thanks for the input! I think I'll switch it on for the added security, and if things go awry, just turn it back off. I appreciate the feedback on this.