I have searched for this but found nothing conclusive. I have my Slack 9.1 on ext3 and wonder if it is possible to convert it to reiserfs without a lot of trouble?

nope. it would require reformating.

I reformated and reinstalled a couple of weeks ago and decided to try reiser instead of ext3, it seems nice so far, marginally faster than ext3.

reiserfs seems more stable and faster than ext3. I always had the odd fsck problem on IPCop ext3 boxes.
I have also seen several reports that when reiserfs does go wrong, it is a total partition loss.
I am looking forward to reiser 4, it looks very good on paper

Thanks everyone. Seems like a decision to be postponed for a while. I chose ext3 over the others for various reasons and I cannot remember them all now. I have heard that business about reiser possibly failing catastophically and have read on the reiser website that reiser4 will need some settling down, so I reckon I will stick to the devil I know for now. I really was only tempted to change so I could use Qtparted as it apparently cannot resize ext3 partitions but can do reiser. I got into a slight muddle when rearranging partitions to install Slack and ended up with an unused bit in the middle which I could not add to the adjacent partition for some reason (possibly because I started with Qtparted and only discovered halfway through that I could not resize with it! - yes I know - rtfm). Would like to do it sometime. I'd better learn about cfdisk or somehing.

Reiser can fail catastrophically but so can most other file systems. Reiserfs seems pretty durable against normal abuse. From what I've seen you're more likely to have a mechanical failure eat your partition.

I like reiser, I switched after I started jacking with somehardware that kept locking my machine, when rebooting after the lock.. fsck would require reboot after reboot and delete some of the files i was using when the machine locked.

After the machine finally crashed I reformatted and chose reiser... I started jacking with my problem hardware and it continued locking.. however.. after 10-15 more reboots, the machine ran fsck in less than 10 seconds.. and I lost no files. I finally gave up on the hardware though..