I have had NOTHING but bad experiences with WordPress import.
1) I tried to upgrade my client's blog to 2.5.1, but could not because the Simple Tagging Import is BROKEN. As described here (http://wordpress.org/support/topic/174519?replies=2) and here (http://trac.wordpress.org/ticket/6505); both of which NO HELP has been offered by ANYBODY, not even a "I don't know, works for me..."
2) So instead my client decided to just move the blog to another server (2.5.1 was going onto a new server, as well), something I did for them a year ago without any problems.
a) Of coarse WordPress DOES NOT export/import correctly through MySQL. I have known this for some time. But I tried anyways, was not too dissapointed when it didnt work the first, second or third time due to the fact that wordpress does not add escape characters to any fields and generates SQL errors for thousands of lines (would take 15 hours to do change by hand, and there is no way to script these mass-changes).
b) I know WordPress import has had it's half of issues, but while trying to upgrade to 2.5.1 the only thing THAT DID work correctly was the posts/categories/comments import. Well not in 2.3.3! It doesn't work! at all!
Note: YES. I Have edited PHP.ini and changed every single value to abnormally high numbers to prevent a timeout in either seconds or upload limits. My file is 30.9 mb and have set 2 settings (I am too pissed off to remember the exact settings; max_upload_filesize and one other) to 40mb.
Why do I hate this import process so much? Well because it is THE MOST ANNOYING ****ING THING IN THE WORLD!
I get through step 1, no problem. It uploads the file, and I can find it in my wp-content/uploads/2008/05 folder. But guess what? It BREAKS after that. It says 'Wordpress Import' with nothing below it, no status message. The only way to get the 'Are you sure you want to do this? yes/no" message is to refresh, but at that point it has lost it's file attachment. When you click yes, it says the MOST annoying message "File is empty. Please upload something more substantial. This error could also be caused by uploads being disabled in your php.ini."
*MIDDLE FINGER* as I look at the file information that CONFIRMS it exists at 30.9mb, in the correct directory, with the correct permissions.
It wouldn't be so bad if there WERE THE ****ING option to select the file manually from your uploads folder, therefor bypassing the entire BUGGY upload process and just move on to the import! BUT NOOOOOOOO, you have to UPLOAD the ****ing file alllll over again, to find another BLANK PAGE and NO STATUS REPORT, ERROR, OR ANYTHING TO HELP YOU OUT!
I apologize for my use of profanity (I censored the words myself) but with 13 hours down the drain AND NO RESULT, it is hard NOT TO BE PISSED OFF. I would normally be more patient, but without any help from this community, and documentation that does not provide troubleshooting, you feel left in the dark. this is especially true when a CORE FEATURE fails on you, despite every attempt.
If anybody, I MEAN ANYBODY, has anything to suggest or throw in here, please do it. I have reached my last straw, and without any help (yet again) this will be an abandoned cause.