When I took over one of my forums it was running PHP-Nuke, was slow as molasses, and members were jumping ship left and right. I quickly converted it to plan phpBB which stopped the hemorrhaging, but it was some time before I had some spare cash for vB.
I still have a few tiny phpBB forums, but I don't think they'll ever be popular enough that I'd need vB.

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Science Chats | Disabled NYC | The Chic Petite

vbulletin from the beginning. when i starting getting on forums, as a user, it was only vB sites, idk why. then i worked my way up the ranks at a vB site to admin. then that admin pushed me to start a forum, and vB was the logical choice...

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Philly Sports
Delaware Online
PA Forums

i was running phpbb3, easy to code and style and was quite secure. But my members didnt like it very much and alot of my members liked invision (competing forums are all invision) so i gave them something different and i liked vbulletin

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Broadcasting World - #1 Broadcasting Forum
A survey has shown that smoking is one of the leading causes of statistics

theres another large DE forum (for fire fighters) im about to advertise on, it runs phpbb3, trying to talk the guy into moving to vB...

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Philly Sports
Delaware Online
PA Forums

should be easy :p

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Broadcasting World - #1 Broadcasting Forum
A survey has shown that smoking is one of the leading causes of statistics

I ran phpBB 2 when I first started, then got fed up with that and went to MyBB, finally I went to vB and 3 licenses later haven't looked back.

Now a days sometimes I'll setup a forum with myBB to see how well it takes then convert later on.

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- Big Dan proprietor of DJ Talk

I starting setting up one using phpBB, but quickly realized the superior product that vBulletin offered. So, after two members joined (me and a friend), I started vBulletin.

Dan, that's a good idea as far as seeing if the forum 'takes off' or not and then convert to vBulletin. Can you actually avoid losing posts and all of that as well when converting?

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Walt Disney Boards
Walt Disney Buddies
Glam Rock Talk : Under Construction :D

phpbb early on.

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Trumpet Forum - Indiana Gun Shops - Indiana Gun Owners

Earlier I was using phpbb on my forum and then switched to vBulletin and ever since I haven't looked back. Though I do run a couple of SMF forums

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Why most forums fail within 1 year!

India Travel Forum | India Travel Directory | Free Travel Directory

Sure, if you turn off the phpbb forum (and make a backup) before beginning the conversion you shouldn't lose any posts. On the other hand, I always manage to lose everybody's avatars

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Science Chats | Disabled NYC | The Chic Petite