Marcy, I answered you in more detail offline, but for anyone not familiar
with the Arboretum:  You're right.  It's a big place.  So, to maximize your
sightings, it helps 
to do several places throughout the park.  

I usually start with the Mt. Hamilton/azalea collection area first.  Check
first around the parking lot and gift shop.  Then, as you walk up from the
visitor's 
center parking lot and walk up the terraced steps, there's a little pond. 
That area's always good to check for warblers and other migrants.  Then walk
along the gravel path until it connects with the paved road that goes up Mt.
Hamilton.  (This area is very thrushy, too.) Follow that all the way to the
azalea hillside, then check around there. Walk back the paved road or
through the azaleas (where I heard the worm-eating yesterday).  I like the
paved road up the "mountain" because the warblers seem to cross back and
forth over it.

After that, if time allows, I usually go back to my car and check several 
other places:  1) at the intersection of Holly Springs and Hickey Hill 
roads, if you turn right and go up the hill to a turnaround and park, you 
might find several interesting birds along there.  There's a little path
along the ridgeline from there that can be good (it was where I had
eye-level views of magnolia and chestnut-sided yesterday), 2) park by the
columns and walk back through the lilacs and/or into Fern Valley.  In
between the lilacs and the edge of Fern Valley is where I heard one of the
blue-winged warblers yesterday and saw one there on Monday. By the way,
yesterday the blue-winged I saw was right by the main parking lot, just over
the iron fence in a bush. 3) Check Hickey Hill for warblers coming up the
slope.  4)  park by the Holly Collection and check out that area briefly.  I
sometimes find good birds in there.

During the week is best because it gets pretty crowded around the azaleas on
weekends, but the other places I mentioned are less trafficked, even on
weekends.

There are a few other regular birders at the Arboretum, so maybe they can
add to this.  Hope this helps.

Tom Jones
Washington, D.C.