So far I couldn't find any other distro using this variable. Any unwanted side effects we have to fear when using it? What do we gain?

NetBSD is using it, and also windows is using a minimum delay in milliseconds.
http://cvsweb.netbsd.org/bsdweb.cgi/src/external/public-domain/sqlite/Makefile.inc?only_with_tag=MAIN

This allows for shorter locks and faster multi process access to a single sqlite db:
http://beets.radbox.org/blog/sqlite-nightmare.html

Side effects, I'm assuming there shouldn't be any but that i can't promise ;)
Also if you download the code from their website and perform the "normal" ./configure && make
The -DHAVE_USLEEP=1 is the in addition to many other flags (which I'm personally not that interested in ;)

Some code from sqlite:
Without HAVE_USLEEP sqlite3OsSleep always waits 1 second before trying again to aquire a lock.

static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
volatile WalCkptInfo *pInfo; /* Checkpoint information in wal-index */
u32 mxReadMark; /* Largest aReadMark[] value */
int mxI; /* Index of largest aReadMark[] value */
int i; /* Loop counter */
int rc = SQLITE_OK; /* Return code */

assert( pWal->readLock<0 ); /* Not currently locked */

/* Take steps to avoid spinning forever if there is a protocol error.
**
** Circumstances that cause a RETRY should only last for the briefest
** instances of time. No I/O or other system calls are done while the
** locks are held, so the locks should not be held for very long. But
** if we are unlucky, another process that is holding a lock might get
** paged out or take a page-fault that is time-consuming to resolve,
** during the few nanoseconds that it is holding the lock. In that case,
** it might take longer than normal for the lock to free.
**
** After 5 RETRYs, we begin calling sqlite3OsSleep(). The first few
** calls to sqlite3OsSleep() have a delay of 1 microsecond. Really this
** is more of a scheduler yield than an actual delay. But on the 10th
** an subsequent retries, the delays start becoming longer and longer,
** so that on the 100th (and last) RETRY we delay for 323 milliseconds.
** The total delay time before giving up is less than 10 seconds.
*/
if( cnt>5 ){
int nDelay = 1; /* Pause time in microseconds */
if( cnt>100 ){
VVA_ONLY( pWal->lockError = 1; )
return SQLITE_PROTOCOL;
}
if( cnt>=10 ) nDelay = (cnt-9)*(cnt-9)*39;
sqlite3OsSleep(pWal->pVfs, nDelay);
}


The functions directly affected by this change will be only these two.

/*
** Sleep for a little while. Return the amount of time slept.
** The argument is the number of microseconds we want to sleep.
** The return value is the number of microseconds of sleep actually
** requested from the underlying operating system, a number which
** might be greater than or equal to the argument, but not less
** than the argument.
*/
static int unixSleep(sqlite3_vfs *NotUsed, int microseconds){
#if OS_VXWORKS
struct timespec sp;

sp.tv_sec = microseconds / 1000000;
sp.tv_nsec = (microseconds % 1000000) * 1000;
nanosleep(&sp, NULL);
UNUSED_PARAMETER(NotUsed);
return microseconds;
#elif defined(HAVE_USLEEP) && HAVE_USLEEP
usleep(microseconds);
UNUSED_PARAMETER(NotUsed);
return microseconds;
#else
int seconds = (microseconds+999999)/1000000;
sleep(seconds);
UNUSED_PARAMETER(NotUsed);
return seconds*1000000;
#endif
}



/*
** This routine implements a busy callback that sleeps and tries
** again until a timeout value is reached. The timeout value is
** an integer number of milliseconds passed in as the first
** argument.
*/
static int sqliteDefaultBusyCallback(
void *ptr, /* Database connection */
int count /* Number of times table has been busy */
){
#if SQLITE_OS_WIN || HAVE_USLEEP
static const u8 delays[] =
{ 1, 2, 5, 10, 15, 20, 25, 25, 25, 50, 50, 100 };
static const u8 totals[] =
{ 0, 1, 3, 8, 18, 33, 53, 78, 103, 128, 178, 228 };
# define NDELAY ArraySize(delays)
sqlite3 *db = (sqlite3 *)ptr;
int timeout = db->busyTimeout;
int delay, prior;

assert( count>=0 );
if( count < NDELAY ){
delay = delays[count];
prior = totals[count];
}else{
delay = delays[NDELAY-1];
prior = totals[NDELAY-1] + delay*(count-(NDELAY-1));
}
if( prior + delay > timeout ){
delay = timeout - prior;
if( delay<=0 ) return 0;
}
sqlite3OsSleep(db->pVfs, delay*1000);
return 1;
#else
sqlite3 *db = (sqlite3 *)ptr;
int timeout = ((sqlite3 *)ptr)->busyTimeout;
if( (count+1)*1000 > timeout ){
return 0;
}
sqlite3OsSleep(db->pVfs, 1000000);
return 1;
#endif
}

Can be closed, was an error in my code, the current PKGBUILD (on my arm system) builds with HAVE_USLEEP=1