Just to make things interesting here, this is a list of what I DON'T like when I surf the web.  This is NOT intended as a flames list, or anything of the sort.  These are just my opinions on certain matters. 

1. I don't like certain things that DEMAND a link back or signing the guestbook (like Web Site Review Sites and Fanlistings, mostly).  I can understand REQUESTING one, but saying "The link MUST be up or I will not review/add you to the fanlist" is just mean in my opinion (for one, for thefanlistings.org fanlists, it's against the rules to not list).
2. Sites that go on Hiatus and NEVER return.  That's one reason why I have this in my tips to keep it up.  I've seen SO many websites that I love go on hiatus and never again see the light of day.  it's sad.
3. Why do you NEED to take the site down when going on Haitus?  You can just put in big bold letters "I am going away/comming up with new layouts/am too busy to update for a bit". 
4. Sites that rip off of other sites, or direct link to their files.
5. Sites that claim to be the #1 on a certain topic.  According to who?  Even if it's hit wise, maybe another site is better, but if people don't know about it as much, they might not know to go there.  You could have the most popular website in the world, that does NOT make you #1 in the subject of your site.
6. WPR's that sugarcoat or have only a grade point scale.  I think WPR should tell people what they think is wrong, and possible ideas to fix it.  Telling someone that their splash page is "nice" doesn't tell them WHY you like it (or don't like it, if that's the case).  Saying "you should put the viewing requirements" or "That image doesn't quite match the background" is a MUCH better method in my opinion.
7. WPR's that take a LONG time to review.  I've seen some that say you'd have to wait as long as a month (because some only review at at certain time of the month or something).  This is a major turn off to me.  Why wait a month when I can wait maybe 3 days?  If you can only devote once a month to review, maybe you shouldn't own/work for an WPR.
8. Sites that have both a pop-up and non pop (or a 1024 x 768) version of the site.   But often, the non-pop or the 800 x 600 version has the backgrounds messed up.   In that case, it's not really made for that resolution!.  It's nice to have separate version for those who don't want a pop or use 800 x 600 still, but at least make it a separate version, instead of just opening the window in that size.
9. All fanlstings should have at LEAST one member at all times.  This would be the person who owns it.  If you created the fanlisting, obviously you are a fan, and therefore, shouldn't you join your own fanlisting?  It annoys me when I check out a newly opened fanlisting and find 0 members there.
10. Another for fanlistings:  Make sure the friggin' join form works!  Test it!   I've run into many fanlsitings that I've tried to join but never could because the join form was broken, and there is no visible e-mail back to the webmaster to join that way or inform them about it.