For both phones have you tried to remove the battery for a bit then put it back in? I know some other users have been having troubles with the market
You might want to try clearing the Market cache too.
Menu > Settings > Applications > Manage Applications > Select "All" in the top toolbar > Market > Clear cache
That's helped me in the past anytime the Market app started acting flaky.
Thanks for the suggestions, I'll try those - I really appreciate it!