>>
>> It is also an extra activation per element of the collection (because 
>> the ifTrue:-block in the original version gets inlined) which actually 
>> shows in a quick benchmark:
>>   "Create a list with 1 million true/false elements"
>>   list := Array new: 1000000.
>>   1 to: list size do:[:i| list at: i put: i even].
>>   "Search for occurances of true by various means"
>>   anObject := true.
>>   tally := 0.
>>   time1 := [list do:[:each| anObject = each ifTrue:[tally := tally + 
>> 1]]] timeToRun.
>>   time2 := [list inject: 0 into: [:tally :each |
>>               anObject = each
>>                   ifTrue: [tally := tally + 1]
>>                   ifFalse: [tally]]] timeToRun.
>>   time3 := [list count:[:each| each = anObject]] timeToRun.
>>   { time1. time2. time3}
>>
>> This results in #(397 590 600) on my machine with the significant 
>> difference that being between ~400ms (original version) vs. ~600ms 
>> (with extra activation).
>>
>> Cheers,
>>   - Andreas

There's an unnecessary assignment in your inject into test. It should be...

  time2 := [list inject: 0 into: [:tally :each |
               anObject = each
                   ifTrue: [tally + 1]
                   ifFalse: [tally]]] timeToRun.

Not that it makes much difference in the benchmark.