I still remember when Google help said GContacs could only support 10k entries, and I had merge two accounts, putting it over 12k.
Plaxo couldn't even pull them via api.
The thing that most bothers me with GC is that anything done on it, feels like it's done after on batches and by a queue/cron.
Also, since it's linked to g+ circles, it's quite messy to know where the details of a person are coming from.
Mix it with a Google Enterprise account, and you get a third source of problems: Directory