hi cmpm,
I have a paid account (I like being able to access my mail from within Outlook and, when I initially purcahsed the upgrade, I got 1 GB versus 25 MB so it was worth it. I'm not so sure it's that worth is anymore...). Anyway, the limitless mailbox applies to both free and paid accounts, so fill your boots!
I like the Yahoo Mail Beta more than GMail - I use it more, anyway. The only thing I like better about GMail is the tagging vs. Yahoo where you still need to use a traditional folder system to organise your mail. Having said that, it's fully searchable, so you probably don't really even need to do that...