- For a long time, the status of other users it showed was completely off. Like showing people online when they weren't. Also, sending messages sometimes mysteriously failed.

- Cannot copy conversation as text (formatting is messed up). Cannot save it as text without removing smileys.

- Cannot paste text verbatim into conversation without making silly smileys everywhere.

- There is a (relatively small) limit on how much text you could paste in.

- Couldn't transfer certain files (like .js or .exe).

Many of these things make sense for things like unmoderated chat, but I need to work, and sometimes exchange larger amounts of text and binary data.

The screen sharing also seems to take a while to sync up. Worse, it silently stops updating somewhere in the call. Lync seems to have the worst real world performance of any screen sharing / conferencing app I've used.

The only reason it can compete is because of Microsofts package deals and the anticompetitive integration with the rest of their ecosystem.