Upgradaded the beginning of a 4.0.18 site to 4.1
(of course all the .18 stuff is fully backed up 
)
Began with a fresh, full install then tried doing a product import via CSV 4.0.18 export. BAM, got an error in
modules/Import_3x_4x/import.php (Line 1569)
Code:
Undefined function: func_recalc_subcat_count ...
This error prevented me from importing products/categories.
I understand there is a pending db patch for 4.0.16 to 4.1, so it may fall into that category;
however, commenting out this line (band-aid) did the trick for me and all products imported fine. Note: 11 products total, so easily verified. I would urge hesitation for users with more items, yet I'm still happy my categories, manufacturers, and products/details all came through fine.
Too bad I didn't read this post until ::AFTER:: the fact. Now I'm in limbo debating whether to roll-back to 4.0.18 (the right move) or to wait for 4.1 STABLE.
Best of luck to ya X-Cart.