Caroline says on 14/Jun/11
My mom is best friends with Pam Fryman, and knows Alyson Hannigan pretty well, and she says that Alyson is about 5´4", perhaps she could need a slight downgrade. Anyways, we got to meet up with the cast last summer, and we hung out at the beach, and everyone was barefoot. I am 5´8" and my mom is 5´9". I was 1" taller than Cobie Smulders, which makes her around 5´7". Neil Patrick Harris had about 2" on me, and Josh Radnor had 2.5". Jason Segel is as tall as his listing here, 6´4". NPH also admitted that they, especially him, are using various lifts and build-ups inside their shoes to make the height difference seem smaller.
So, NPH (5´10"), Radnor (5´10.5") and Smulders (5´7") should all be downgraded.
Wish I had some pictures to back this up, but the only ones i´ve got, we are all sitting down.

KK.12 says on 29/Apr/11
She is 5'4"- on How I Met Your Mother, Marshall is said to be 6'4", and he has at least 9 inches on her when she's wearing heels. When she isn't, he's about a foot taller than her.

Stephanie says on 26/Mar/11
I always thought she was 5' 4".

Jayjay says on 26/Dec/10
Sara: Cobie Smulders is 5'8", Alyson H is barely as tall as her in heels, so no, she is no enere close to 5'7" or 5'8". Alyson hannigan is tiny, 5'3.5-5'4" max!