Alot of people are reporting bugs because something is missing but it may just be moved to a new place. So here's a list of commonly asked questions and where to find them or what their status is.

Where is my dashboard?
The dashboard is now called the "home" page it is available by clicking the last.fm logo in the upper left or from the dropdown in the upper right of the page.

Where is my profile page?
Just click you username in the upper right of the page.

Is there an option for making the theme black?
Currently there isn't but the staff have hinted about it coming back. In the meantime the only alternative is a greasemonkey extension.

How come my charts aren't 50 tracks any more?
Click on "settings" in the upper right of the charts for customization options including upto 50.

How do I set my charts to something besides the last 7 days?
Same answer as above. Click "settings" and choose your chart measurement.

I want "weekly" charts that end on Sunday again.
This option is not currently on the front page charts. Click on the "charts" tab on the left and from there you can get your "weekly snapshot" chart.

Where is "paste your taste"?
This is currently not available, but is likely to return shortly.

What is the point of the library? It's just a bunch of images of artists I already know.
The library is like you personal database of tracks you've played. Artists can be permanently removed by clicking the x that shows up when you hover over the artist. Click on the numeric value or check the "in my library" button on artist pages for more info.

How come my library just shows my top artists? They don't change very often.
Click on "settings" for the library to change the chart list for what artists show up or choose your own 8 artists that best represent you.

I feel the 'recent activity' feed is a threat to my privacy.
The 'recent activity' feed settings are located here, where you can choose who is able to see the 'recent activity' part of your profile. The default setting is for everybody to be able to see it, but you have a two week 'grace period' from the launch of the new site before this takes effect, during these two weeks it will be hidden from everybody other than yourself unless you manually change the settings.

How do I keep my finger from getting sore from constantly having to scroll down to my shoutbox?
Click on the "shouts" button at the top of your profile to jump down to the shouts.

How do I tag, love, or add to my playlist for an artist/album/track/label?
The "more" button with the gear next to it has these options.

How come I can't play playlists?
Due to licensing laws playlists have become subscriber only features. Even if they're not your own.

I can't go over 200 tracks on a playlist.
Playlists are restricted to 200 tracks per playlist. Old playlists that had over 200 tracks are currently cut off but the issue is being looked at by the staff.

My charts used to go to 500, now they only go to 200
Currently that's the biggest available. Staff are planning to change this.

Where did my new messages go?
The notification of PMs is now on your homepage or next to the "inbox" in the dropdown menu in the upper righthand of the page. (it's back where it used to be, up on the right)

Where did weekly neighbors go?
Currently missing. Staff will have to comment, I don't know where they are.

Where are artist tag clouds?
In the "tags" tab on the left of artist pages.

How do I add images to albums missing art?
Currently missing. Staff will have to comment.

Where are recommendations?
They have their own page accessed from your home page, or from the dropdown in the upper right. The system has been upgraded and more info is provided about why last.fm thinks they're similar to you.

Where are the country pages?
They're not available just yet, but staff say they are going to return. (they're back)

How come "Disable images" isn't getting rid of pictures?
It seems to currently be inoperable. Staff will need to comment on how long it will take to get back. (officially gone :( )

How come my personal recommendations aren't on the recommendation page?
They have been moved to your inbox and are designated with a music note icon.

Where are group recommendations?
Currently not available.

How do I add events?
Currently the button is in the upper right hand side of the "events" page. This button will be coming back to artists and venues in the future.

What is the "application" tab in settings for?
Future development.

Can we revert to the old last.fm?
No. Sorry. The new site is designed to make use of new features in this revision and future revisions.

Also check the "Known Issues" sticky for more items that may be missing.

I've updated this slightly.

Hope you don't mind that I've also altered the title, but I agree with the thread that suggested "Bring Back *blank*" doesn't necessarily make it clear exactly what's contained here, "Site Update FAQ" should hopefully draw more people to look in here before posting questions which are answered in this thread.

For anybody interested, this is the staff post which says the top 500 should be returning [edit: top 500 now back!], and this is the staff post which says that country pages will return.
This post is the one suggesting the return of 'paste your taste'.