If the problem continues I'd go to your BIS account, delete the e-mail account, and then re-add it. Sometimes that does the trick. If not just has something to do with Yahoo. I get that happening from time to time.
I am having the same problem on my Curve in Los Angeles. Sometimes no sycn with yahoo, and sometimes it works very slow. Its been like this for two days now.
Thanks for the confirmation. Must be a BIS-Yahoo issue. Lets hope they get this resolved. If not, tomorrow I'll get AT&T's support to submit a report w/RIM.
Im glad all you are posting this, I thought it was just me. Noticed the bad lag yesterday and today. Sometimes it takes a few hours, sometimes its almost instant.