I am up to RC2, no problems.
There is noise at Mozillazine that some people are finding that saved passwords disappear. I have had no problems. Someone there entered this as a bug report.
But, alas, for now, I am abandoning SM as my default. It looks like I found the problem I had in FF with my ISP's web mail:
In Privacy, if I select "Remember history", FF "remembers" the email addresses I have typed in the web mail. If I select "Use Custom Settings", even if I have "Remember search and form history" checked, FF does not remember the email addresses. With "Remember history" selected, I sent a bunch of test emails to various email addresses I have at Google, MyYahoo! , etc. Then I rebooted and FF h remembered, which means type in one letter and every address staring with that letter pops up, same as in MS-Outlook. Testing through a re-boot is generally the benchmark.
If it fails again, I will again go to SeaMonkey.
>>RSM
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.1.3) Gecko/20090824 Firefox/3.5.3 (.NET CLR 3.5.30729)