I have a little study on this (very little, and not at all scientific),
between my neighbor and myself.  Her son was completely bottle fed, mine
completely breastfed.  Both were full-term, healthy babies.  Mine is 2 1/2
months older.  Hers started eating solids earlier (don't know exactly when,
but probably pretty close to the 4 months recommended by a lot of peds).  He
was quickly eating a large quantity of jarred baby food.

I actually tried to introduce solids at 4 1/2 months (I thought he was giving
cues that he was ready), but my son flat out refused them.   I tried on and
off for several months, but the day he force vomitted, I decided to quit and
just let him feed himself when he was ready.  From then on, I would always
put him in the high chair when the family ate, put some appropriate food on
his tray (something from the families meal, not "baby food"), and let him do
with it what he wanted.  He was 10 months old before he started putting
anything in his mouth, and 16 months before he was eating any significant
amount of food (enough where I felt it was safe to say that he was really
getting anything from it).

My son is now 3 (actually, will be 3 on Saturday).  He eats a wide variety of
foods and there is almost nothing he will not try.   He loves fruits and
vegetables espeically.  My neighbor's son was still eating mostly baby food
when he was 2--she couldn't get him to eat anything else.  He refuses most
fruits and vegetables--his diet consists primarily of things such as corn
dogs, fast-food burgers and fries, and sodas (when she told her ped she could
not get her son to drink anything but milk and Diet Dr. Pepper, her doctor
said that was fine, if that was the only fluid he would take, it was better
than nothing---ack!).  If he eats a fruit filled pastry, she counts that as
eating fruit.

We are now embarking on our second study--we both have 2 month old babies
(less than 2 days apart in age), so check back in another year for an update
:)

Oh, one more point--I nursed my toddler during my pregnancy.  When I got
pregnant, he was nursing at least 10 times a day.  He also ate a fair amount
of solids, but his solids consumption *tripled* when my milk dried up in my
second trimester.  Now that my milk is back, he is back to nursing as much as
he can (will nurse more than the baby if I let him), and his solids
consumption is back down to the level it was at when I got pregnant.  None of
this has affected the babies growth at all--he has been gaining 8 ounces a
week (which is the same growth pattern my first son had for the first 2
months).

Sorry to go on so long, but I am very interested in the topic of
solids/breastmilk and have thought a lot about these things.  Not too
scientific, but still interesting.

Susan Smylie