I have just installed 11.04 via wubi and will tell you how it works for me.

There are two upgrade paths with Ubuntu, LTS to LTS (long term support)
which you are not using and normal releases. The last LTS was 10.04 and the
next one will be 12.04. Your choice is to upgrade through each version or
stay pat until you have to upgrade next April, then reinstall.
So you need a reason to upgrade.
If you want to try 11.10 which comes out October 13th then you must go
through 11.04 first.
There are no real problems with 11.04. Some don't like the default
interface, but you can still use the old one if you prefer.

The biggest issue with 11.04 is that the Unity user-interface is not as polished
as it will be. At logon you can choose "Ubuntu classic" if you don't like it.

For people with new hardware, there are big improvements in (especially laptop)
audio and (especially USB) wireless hardware support. If your audio and wireless
work fine in 10.10, and you don't want to see how Unity works, there's no real
reason to change.

In another month, 11.10 will be available. Unity will be more mature in that
release.

I have never done a version upgrade, as a clean install is less likely to cause
problems. It's a lot easier if you have separate root and home partitions, which
is set up at install time.

I down loaded 11.04 via wubi. it took 5 hours even on my fast connection
but it works fine. I like the interface so far. it easy to see and work on.