Another one in Ruby, 573 546 characters
:**
Z={I:?#*4,J:'#,###',L:'###,#',O:'##,##',S:'#,##, #',Z:' #,##,#',T:' #,##, #'}
t=[*$<]
R=->s{s.reverse}
T=->m{m.transpose}
a = T[R[t].join.scan /.#{'(\D)'*10}.$/]
t.pop.split.each{|z|
t,o=Z[z[0].to_sym].split(',').map{|x|x.split //},z[1].to_i
r=0..t.size-1
y=r.map{|u|1+a[o+u].rindex(?#).to_i-t[u].count(' ')}.max
(0..3).each{|i|r.each{|j|t[j][i]==?#&&a[o+j][y+i]=t[j][i]}}}
s=0
a.each{|x|s=a.max_by(&:size).size;x[s-=1]||=' 'while s>0}
a=R[T[a].reject{|x|x*''=~/[#]{10}/&&s+=10}.map{|x|?[+x*''+?]}[0..6]]
puts (0..8-a.size).map{?[+' '*10+?]},a,s
Testing:
cat test.txt | ruby 3858384_tetris.rb
[ ]
[ ]
[ ]
[ ]
[# ###]
[# ### ]
[##### ####]
[==========]
10
