Okay. I am pretty convinced that exporting PDFs via export command is horribly broken in Mathematica 9.
Show[Plot[x^(1/2), {x, 0, 10}, PlotRange -> {{-0.4, 10}, {-0.35, 4}},
PlotStyle -> {Thick}, Ticks -> {{0}, {0}},
AxesLabel -> {Style["l", FontSize -> 14],
Style["\!\(\*SuperscriptBox[\(f\), \(T\)]\)", FontSize -> 14]}],
Plot[(2^(1/2) x)/4 + 2^(1/2)/2, {x, 0, 10},
PlotRange -> {{0, 10}, {0, 4}}, PlotStyle -> {Red},
Ticks -> {{0, 2, 4, 6, 8, 10}, {1, 2, 4}}],
Plot[(6^(1/2) x)/12 + 6^(1/2)/2, {x, 0, 10},
PlotRange -> {{0, 10}, {0, 4}}, PlotStyle -> {Purple},
Ticks -> {{0, 2, 4, 6, 8, 10}, {1, 2, 4}}],
ListLinePlot[{{2, 2^(1/2)}, {2, 0}},
PlotRange -> {{-0.5, 5.5}, {-1, 10}},
Ticks -> {{0, 1, 2, 3, 4, 5}, {0, 5, 10}},
PlotStyle -> {Black, Dashed}],
ListLinePlot[{{6, 6^(1/2)}, {6, 0}},
PlotRange -> {{-0.5, 5.5}, {-1, 10}},
Ticks -> {{0, 1, 2, 3, 4, 5}, {0, 5, 10}},
PlotStyle -> {Black, Dashed}],
Graphics[Text[
Style["\!\(\*SubscriptBox[\(l\), \(old\)]\)", Black, Bold,
Larger], {2, -0.15}]],
Graphics[
Text[Style["\!\(\*SubscriptBox[\(l\), \(new\)]\)", Black, Bold,
Larger], {6, -0.15}]]]
Export["figure11.pdf", %, "AllowRasterization" -> True,
ImageSize -> 360, ImageResolution -> 600]
The above code produces a 5KB PDF when run in Mathematica 8.04. The same code produces a 2.9MB PDF file when run in Mathematica 9.01. Both PDFs look exactly the same.