Interface slow/buggy with two user accounts?

A trip might be in order but not yet. First run software update, if your profile is correct you're a version behind as 10.6.8 is current, there may neither updates as well. Second reset the SMC and pram

To reset the SMC

Shut down the computer.

Unplug the computer's power cord.

Wait fifteen seconds.

Attach the computer's power cord.

Wait five seconds, then press the power button to turn on the computer.

To reset PRAM/NVRAM

Shut down the computer.

Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.

Turn on the computer.

Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.

Hold the keys down until the computer restarts and you hear the startup sound for the second time.

Release the keys.

And by creating the second user account you've ruled out that the problem is corrupt user prefs. The account isn't hurting anything and if you ever need to test again you've already got the account. I always have two user accounts on mine.

Mike provided PRAM reset instructions but may have forgotten the SMC reset, please click iMac SMC and PRAM reset. Also you may have some corrupt caches, click Safe Mode reset for instructions. All are pretty simple to do and may help.

I forgot about a safe boot rkaufman, thanks

You also may simply be low on RAM and need to upgrade. You can keep Activity Monitor (Applications - Utilities - Activity Monitor) open and when you notice a slow down, click the System Memory tab and check the amount of FREE RAM. As a general rule of thumb if the system has 500MB or less of RAM that could indicate the system needs more RAM. It will look similar to:

...if the system has 500MB or less of RAM that could indicate the system needs more RAM.

The amount of free RAM is no indication of the need for more RAM. Ideally, it should always be zero, if RAM is being fully used.

Activity Monitor: Check whether more RAM will improve performance

I agree at 12GB it has enough RAM however keep Activity Monitor open and look to see when it slows if you have a process using a larger %CPU. You could have a problem with an app. Let us know what happens.

Better off opening Terminal and entering "top." The figure in AM is cumulative, while the figure in parenthesis using "top" will show Page outs in real time.

Linc Davis wrote: The amount of free RAM is no indication of the need for more RAM. Ideally, it should always be zero, if RAM is being fully used.

??? Can you please elaborate on this. In my experience, very low free memory is usually accompanied by a large Swap file, Page outs and things generally slowing down or possibly freezing. And inactive memory, which, in theory, is supposed to be available for any other apps that need it, it doesn't appear to work this way in practice.

See the support article linked above.

I've read that and already knew all that. But I don't see how that begins to relate to the question I posed, re. your statement that zero free RAM available is ideal if RAM is being fully used. What makes that ideal?

Sounds like a tautology. By definition, at least, if all the RAM is being used, then zero will be available. But again, why is that ideal?

I.e., if all the free RAM is being used and some application needs more or some newly opened application wants some, then the next step is for paging to begin, since any that's in inactive can't usually be relied upon. That doesn't sound ideal.

Or maybe another way of asking this is if it's ideal that all the free RAM be fully utilized, why or under what conditions wouldn't it be?