Challenges to realtime depositions?

Usually, when attorneys schedule a realtime court reporter to cover a deposition, they are prepared and know what the reporter is going to need to get the job done. The worst that usually happens is that two people start speaking at the same time. If that happens, politely interrupt and ask them to slow down - after all, you're responsible for making all of the information available.

The previous answer said it well; in addition to making sure that the lawyers aren't speaking over each other or the witness, make sure that you're asking for clarification when you need it - the spelling of people's names, common acronyms, or if words in a foreign language are used and you're not sure how to document them.

Also, always ask the firm you are reporting for to give you any prior transcripts in the case with word indexes. Having those, you can make briefs and enter them in your dictionary ahead of time.