I just bought a specialized tricross. It has sora in front and 105 in the rear.

Will this cause me any problem? My LBS told me he could not put tiagra or 105 shifters on the handlebars because they are 9 speeds. Is it possible eventually to convert to 105 all around or will I be stuck with sora forever?

Right now I only used the bike for 30 minutes on a trainer. It seems to shift well enough. The rear 105 will shift to any speed without any problems. The front sora requires me to lift off from the pedals a little when going from the small platter to the big one.

I have an Ultegra 9 speed bike, and had a Sora 8 speed bike. In the front, I noticed a VERY, VERY, VERY slight efficiency in shifting...not enough to spend the extra $ to upgrade the Sora FD to 105. If you don't like thumb shifters, get Tiagra at least.

Also, you should try not to shift under load (sometimes, this is not possible...for instance, on a hill). The rear derailleur will shift better under load than the front, but if you want a smooth, quiet shift, always lessen the load on the pedal when shifting to keep the drivechain working properly for a longer period of time.

I own three bikes,
1) full Ultegra
2) 105
3) Sora
The difference between #2 and #3 is very minimal, IMHO not worth an upgrade.

IME Sora and 105 are very similar, the difference mostly being slightly lighter and better polish and finish on the 105 stuff. I don't think you'd notice a performance difference upgrading from Sora to 105. They're both very good and very usable. You'd have to jump to Ultegra or Dura Ace before you could really feel much difference.

I've tried my sister's Sora-equipped bike. It shifts and brakes just fine. Yes, my Tiagra bike is nicer. And yes, my Ultegra one's even nicer. They require less finger effort, but even the Sora bike shifted cleanly. For bikes in that price range, the upgrades you're contemplating down the road just don't make sense economically.

Especially for a commuter, don't change it unless/until it breaks/stops working.

On the front, WHO CARES!!! IMHO, front derailleurs of ANY make/quality/price are virtually identical. They either work or they don't. If it works, it's as good as anything else.

REAR derailleurs, on the other hand, seem to improve with price. I think it's the closer tolerances and better design, but I'm just speculating. I do know that I can tell the difference between my XTR and an LX just by the way they shift.

Live with the front so long as it works. When it dies, buy a Campy Record off e-Bay for $20 and you'll be set.

I hated my right Sora thumb downshift lever. I could never figure out how to reach it without weird contortions from the drops.

Niether of the above for me.
For the front, an old Suntour derailer with an old school friction thumbshifter.
For the rear, an older model Shimano index derailer, a no-name Sram clone 6 speed twist shifter, 9-speed Sachs chain, and a cassette to match. You may not think it, but it shifts super smooth and spins silent, even in the granny gear/small sprocket combo, and hasn't broken yet.
The retrogrouches might be onto something.

I think the Sora front derailluer is adequate and only fell off the chain once this year (My fault) in hundreds (maybe thousands) of successful shifts. I consider that a very good product.

The OP said the bike is used only on the trainer? Why would you want to upgrade if the bike stays indoors all the time? I can see if the FD was giving you problems when approaching hills but that is the case.

Your Sora is 8-speed, so you will need a nine-speed cassette and chain to upgrade to 105. But your Sora stuff will be fine. If it breaks, you can upgrade then, or replace it cheaply.

I mean, sheesh, most people actually ride the bike on the road a bit before they get caught up in the upgrade-itus...!

Oh... forgot to mention... after a bit, your bike will start shifting badly - this is not Sora sucking, it's "cable stretch" - either fix it yourself or take it to the LBS to be sorted, and you'll be good as new again.

My LBS is giving me a free adjustment in 3-4 weeks. He already warned me of the cable stretch problem. Thanks.

Any good web links explaining how to adjust this myself?

https://www.sheldonbrown.com/repair/

there's also some good stuff at parktool.com