Hi Nick, 
    I have looked through the archives and tried what I found, including the linum-mode and property-inheritance, which didn't affect the problem. I also tried to change to the latest version of org mode and (I think) emacs, which didn't help. I don't recall seeing the font-lock problem, though I may have tried it earlier. I'll look for that one again. Most of the archive questions had a slow agenda all the time, and not only sometimes. 

   I tried your commands below (thank you!) and have some interesting results, but I don't know enough to interpret them. If I am interpreting right, org-scan-tags  sometimes takes much longer, but I have no idea why it would be fast sometimes and slow others. 

Here are the top 10 listings when operation is fast (about 3 seconds) 

Function Name                                                 Call Count  Elapsed Time  Average Time

============================================================  ========== 

org-agenda                                                    1           1.943013      1.943013

org-agenda-run-series                                         1           1.590022      1.590022

org-let2                                                      2           1.1610179999  0.5805089999

org-tags-view                                                 1           0.826727      0.826727

org-scan-tags                                                 5           0.760431      0.1520862

org-let                                                       2           0.426281      0.2131405

org-agenda-get-restriction-and-command                        1           0.3529        0.3529

org-agenda-list                                               1           0.334261      0.334261

org-prepare-agenda-buffers                                    2           0.3264879999  0.1632439999

org-prepare-agenda                                            3           0.3113339999  0.1037779999

org-get-entries-from-diary                                    1           0.266385      0.26638


When agenda is slow: 

Function Name                                                 Call Count  Elapsed Time  Average Time

============================================================  ==========  

org-agenda                                                    1           12.133429     12.133429

org-agenda-run-series                                         1           11.768025     11.768025

org-let2                                                      2           10.856247999  5.4281239999

org-tags-view                                                 1           10.427989     10.427989

org-scan-tags                                                 5           10.402578000  2.0805156000

org-let                                                       2           0.908944      0.454472

org-finalize-agenda                                           3           0.8176239999  0.2725413333

org-agenda-get-day-entries                                    10          0.6845889999  0.0684588999

org-agenda-get-scheduled                                      10          0.4447109999  0.0444711

org-agenda-list                                               1           0.428234      0.428234


On Sun, Nov 13, 2011 at 2:58 PM, Nick Dokos <nicholas.dokos@hp.com> wrote:
Susan Addy <susan.e.addy@gmail.com> wrote:

> Thanks Bernt. I checked and Linum-mode is not enabled. 
>   
> Also, I using emacs 22.3.1 and org-mode 7.7 (if it helps). 
>  
>
> On Sun, Nov 13, 2011 at 2:16 PM, Bernt Hansen <bernt@norang.ca> wrote:
>
>     Susan Addy <susan.e.addy@gmail.com> writes:
>
>     > Below is a list of my agenda command - maybe it is too long? When it
>     > is slow, it is slow no matter what TODO I am trying to compile.
>     >
>     > Any thoughts? 
>     > Thank you!
>
>     If you have linum-mode enabled you should turn that off.  Others have
>     reported slow navigation when that is enabled.
>
>     HTH,
>     Bernt
>
>

There have been various discussions on agenda slowness in the past -
check the mailing list for some guesses (linum-mode, font-lock, property
inheritance, code compilation and perhaps others have been suggested as
possible causes). Sometimes the guesses pan out, sometimes not.

The most important thing you can do, imo, is to profile the code, first
when it's behaving well and then when it's behaving badly.

All you have to do is

   M-x elp-instrument-package RET org RET

run your agenda command and then

   M-x elp-results RET

to get the results.

Nick