My account hosting suspended this morning, i get this message from my hosting tech support:
"Your account was suspended by the technical department and the reason is it caused heavy server load - MT. But, this time it was mt-search cgi script which is an optional part of Movable type that was causing the load. Perl scripts always take more resources compared to PHP and are not server-friendly.
I would recommend you disable the mt-search. As a long term fix, I think you should start looking for a PHP/MySQL blog. If your account continue to causing high load and you have more members/visitors than a shared server server can hold, you may want to look into upgrading your account to a dedicated plan."
Is this true, should I better use wordpress then MT?
FYI, I got about 1000 visitors on my blog daily.

It is not really the number of users but what they are doing, searching is an active action.
Do you use tag clouds on you page? These are links to mt-search. A search engine bot hitting you page would follow these causing lots of searches in a short time.
Are you getting hit by spam bots that are filing your activity logs we spam searches?
As far a resources go it all depends how it was written
I had the same experience under 3.x due to the constant churning of search spammers (yes, search spammers) and the size of my blog. I changed the default search to use Mark Carey's FastSearch plugin instead and that took care of it. Not ideal, I know, since it would be nice for the default to be able to handle it, but the plugin is quite good, and fast.
I strongly recommend an upgrade to MT 4.2 release candidate 1. Your hosting providers complaints are valid, even if they are technically inaccurate.