As others have alluded to, end user security is the biggest problem IMO.  It would be nice if the bitcoin wizards could just program away the hackers and scammers and protect end users from themselves but that is easier said than done.  I do feel confident that eventually a hardware and/or software "killer app" solution will be designed to do this without the requirement of third party trust.

I would like transaction times of below one second. That would be very powerful. And I would like to have the coins stored safely on the block chain without me having to do cold storage myself or having to trust a third party storing the coins for me. And I would like to have zero transaction fees for all transactions. The price/performance of information technology is improving exponentially and having to pay for transactions feels like the old fiat systems.

Security! It's still too easy to actually scam people out of their money. There has to be simple way for people to protect their Bitcoin without having a degree in cryptography. People are gullible and easily manipulated, too.

1. lack of support from payment processors to go out and do sales pitches to businesses:-
 i have personally told bips, bitpay and coinbase of 5 merchants that wanted more info. and as of yet (upto 1 year in one case) the merchants have not had a single response from the gateways

2. software is still in beta phase and not ready for average joe (7billion population) daily spenders:-
a truly trusted service that actually adheres to consumer protection guidelines (liability insurance to protect customers holdings) to then be used as a offchain service for pre-confirmed funds, making it an instant use wallet to send funds as small as 1sat to merchants.

3. hardware/cold wallets are still in beta. yes trezor(hardware) and HD-01(coldstore) are still not 100% secure or easy to use for long term large storage.

4. bitcoin protocol is not ready to handle heavy volume, it is also not adhering to consumer requirements, but it is more twisted in favour to miners greed.
lets see 'death and taxes' appear with rebuttals to defend the miners honour, like always

in short, we are still in the innovator/early adoption stage.. we have a long way to go yet before being in the mass adoption: public stage

if it was a professional site with proper profile bio's such as a linked in listing. with a jobs listing section with good display of information, and not a simple 'craislist' jobs site. id use it.