I actually had Tiagra on my Allez, and 105 on my TCR. Both 9 speed IIRC. I didn't really notice any difference in shifting between them, except that the 105 was a compact double and the Tiagra was a triple. I only used the Tiagra for a few thousand miles, so I can't attest to it's long-term durability. The 105 shifters on the other hand, were pieces of crap. I killed the rear lever, replaced it, then killed the new one. F-that, I switched to SRAM and never looked back.
I almost feel compelled to own a SRAM equipped bike. Really.
Again, like I posted in my "Double Tap:* thread weeks ago, when so many
people are so passionate about something, it warrants investigation.
I'm pretty sure I'll own a SRAM bike one day.
*
http://www.bikeforums.net/showthread...962-Double-Tap...