I think I've said it one million times to customers and collegues, but I must state it again: Don't use frames - here is 10 more reasons:
10. iFrames is still frames and is not supported by all browsers
9. There are ribbon campaigns to get rid of it - they are ugly and why should good sites be infected with ugly ribbon gif's
8. Bookmarking requires instructions for most users
7. Also with printing
6. Some search engines won't play nicely
5. Big legal nasties could ensue if you're deeply stupid or just don't care
4. It continues to encourage bad webdesigners to do bad interaction design
3. The messy ucky frustrating I want to chew glass reality of working with them
2. Jakob says no way
1. You could owe $50,000,000.00 in retroactive fees to people like SBC. The patent is here.