Being asked to "verify direct XXX"

I'm a new IFR pilot, having gotten my ticket end of January.

One thing I've quickly picked up on is that ATC pretty much expects
everybody to be able to navigate direct. If you tell them you've got a
VFR GPS (in your remarks), they'll happily give you direct clearances
and instructions while airborne. I've learned to deal with that (by
really learning how to use my GPS), though I really still wonder about
the whole thing and marvel at the fact that they'll expect me to
navigate under IFR with this thing without a current database (I don't
keep the DB current and there's certainly no reason at all they should
expect that I do). (I am planning to do somewhat regular DB updates
from here on out, but it's not going to be every month.)

Anyway, on to my question. A couple times now, when I've been
navigating direct, either to a fix or airport identifiable by VORs or
one that isn't (such as an uncontrolled field with no navaid), I've been
asked to "verify direct XXX" when I'm off course by a quite small amount
- no more than 10 degrees. Or, perhaps, I've gotten off course a bit
and have a larger heading correction (20-25 degrees) in to get back on
track, momentarily. I've never had a controller sound annoyed, but it
does concern me a bit that they see fit to more or less ask "Are you
sure you know where you're going"??

I've vowed to put a stop to this, and I have realized that I should
probably pay even closer attention to my heading. I am meticulous about
holding alt but, obviously, heading is important too. Flying
single-pilot IFR with no autopilot, with turbulence, it can be a
challenge in those moments where the workload is high for a bit..

My two-part question is 1) Should I be concerned at all by being asked
such a question by ATC? And 2) Just _what_ is the IFR "heading
tolerance", anyway?? Meaning, what sort of heading deviance is large
enough that you can be violated for it? Does such a figure even exist?
I expected this to be something fairly simple to find in the regs and
it was not.

TIA.

~Paul Folbrecht
~PP-SEL-IA
~'79 C152
~MWC