Dan, i've owned one for 7 years and JUST sold it with 96k miles on (it had 11k when we got it)!
Averages 30mpg all day long, slightly more if you're careful.
Slow indeed maybe sluggish is a fairer word though, but comfortable, good on a motorway at cruising (34-35mpg) and will sit at 80mph very nicely.
Water pump should be replaced as the original had a plastic impella (sp?) but was replaced with an upgraded Metal one - This was a known problem and mine was done under Warranty when the car was just 2 years old but it shouldn't be a massive job.
Cambelt change is pretty simple, £150 at my local garage (not VW dealer).
Look out for the Engine Management light being on, it's a VERY common issue as the Cat is part of the flexi pipe at the front so when that starts to go you have to replace the whole thing including the Cat which is about £450 all in for a genuine VW part. I had 2 non-vw ones and after 2 weeks each time the engine management light would come on again which drove me mad so i ended up getting them to give me my money back and fit a genuine VW part which sorted the issues.
Rear bushes wear around 80k miles, best replaced with the Skoda Fabia ones - far better design and should last forever then (just about).
Brakes i replaced twice, bang on 40k and bang on 80k, around £120 all in for all new Discs and Pads from Eurocarparts or GS+F.
The 2.0l 8V is known to drink around 1L of oil between 10k services but mine was well looked after, always run on decent fully synth oil and never had an issue - maybe 500ml top up after 8k miles just to get it through to the next service.
Over all it's a good car, never going to set the world on fire but even after 96k miles it still drove and felt as good as it did at 30k.
Obviously i spent money on it to keep it in good condition but i really can't fault it for the time we owned it, and people LOVE VW Golf's so will always be someone out there willing to pay for it!
I sold mine for £2850 which i think was fair.
Let me know if you have any more questions on it but hopefully that gives you a good starting point.
Some pics of mine here:
http://www.detailmycar.co.uk/Lightbo...W+Golf+Mk4+GTI